Renewable Energy Global Innovations features: Probabilistic small signal stability analysis with large-scale integration of wind power considering dependence

Significance Statement

Reference to an increase in the wind power generation, power system stability and reliability has been affected by the wind farms. The attributes of winds farms have been observed to be different from the normal power plants, such as thermal or nuclear and hydraulic. Intermittency characterizes wind power and consequently introduces many uncertainties in the electric power systems. Therefore, for optimal operation of the power systems integrated with more sources of uncertainties, it is important to incorporate probabilistic models in the management systems.

Probabilistic methodologies proposed in most studies are perfect for the analyses of uncertainties, in order to account for the uncertainty arising from the generation of wind power. The methodologies are also important in modelling the uncertainty from the loads. More research works have focused on how conventional power systems made of synchronous generators respond to wind power integration, and how their electromechanical modes of oscillation are affected.

The results of the effect of various levels of wind power integration to a system’s small signal stability reveal that the small signal stability is affected negatively when the wind power penetration is increased. On the other hand, similar analyses reveal that wind power integration has both negative and positive effects on the system’s small signal stability.

Keyou Wang and his colleague from Shanghai Jiao Tong University presented a critical and timely review of the methodologies used in the probabilistic small signal stability analysis and dependence modelling. They also presented in their work, a comparative analysis of these methodologies and preferences of the methodologies under various wind power integration scenarios. The report is now published in Renewable and Sustainable Energy Reviews.

Wind turbines do not participate directly in the electromechanical oscillations in power systems; however, they affect the small signal stability by altering the power dispatch to synchronous generators as well as transmission networks. An evaluation of how sources of uncertainties affect a system’s small signal stability is fundamental for optimal operation.

A variety of methodologies has been proposed to account for the uncertainties, and can be classified into three categories: numerical, analytical, and approximate methods, which are represented by the Monto Carlo simulation, cumulant-based method, and point of estimation method, respectively.

Point of estimation and cumulant-based methods have been identified to be better due many advantages. However, the cumulant-based method demands less deterministic simulations as compared to point of estimation method.

The authors realized that accounting for the dependence between the various uncertainty sources was necessary in a bid to determine dependency structures that bear the actual state of the system, and consequently, after carrying out the small signal stability analysis, the outcomes would bear the actual response of the system to small perturbations taking into account dependence and uncertainty.

Out of all the dependence modeling methodologies considered, the pair-copula was identified as the most accurate but time consuming. It was suitable for power systems with small-scale wind power sources integration, and linear correlation coefficients as well as normal copula models were less accurate but were more efficient in large-scale power plants with large-scale wind power sources integration. Therefore, the choice of dependence modeling methods would largely depend on the scale of wind power integration, efficiency and accuracy needed.

About The Author

Jin Xu (S’16) received his B.S. degree in electrical engineering from Sichuan University, Chengdu, China, in 2013. He is currently pursuing the Ph.D. degree at Department of Electrical Engineering School of Electronic information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai, China.

His research interests include power system dynamic modelling and stability analysis, electromagnetic modelling and simulation.

About The Author

Peter Kairu Kanyingi was born in 1986. He received his undergraduate degree in Energy Engineering from Kenyatta University in the year 2011. In the year 2016, he received his MSc degree from Shanghai Jiao Tong University with a Major in Power Systems and its Automation. From Sep 2016 to March 2017 he was with the Department of Renewable Energy at Jaramogi Oginga Odinga University as a part time lecturer. Currently he is a lecturer in the Department of Energy Technology at Kenyatta University, Nairobi Kenya.

His major research interests include power system stability, probabilistic modeling of power systems, modeling of complex dependence and uncertainty existing in renewable energy sources, analysis of the impact of wind and solar power integration into existing power systems, smart grid, HVDC and power system design, modeling and simulation.

About The Author

Keyou Wang (S’05–M’09) received the B.S. and M.S. degrees in electrical engineering from Shanghai Jiao Tong University, Shanghai, China, in 2001 and 2004, respectively, and the Ph.D. degree from the Missouri University of Science and Technology (formerly University of Missouri-Rolla), Rolla, MO, USA, in 2008.

He is currently an Associate Professor and the Deputy Department Head of Electrical Engineering with Shanghai Jiao Tong University. His research interests include power system dynamics and stability, renewable energy integration, and converter dominated power system. He serves as an Associated Editor of IET Generation Transmission & Distribution.

About The Author

Guojie Li (M’09-SM’12) received his B.E. and M.E. degrees in Electrical Engineering from Tsinghua Univ., Beijing, China in 1989 and 1993, respectively. He also received PhD degree in the School of EEE, Nanyang Technological University Singapore in 1999.

He was an associate professor in the Dept. of Electrical Engineering, Tsinghua Univ., Beijing, China. He is now a professor in the Dept. of Electrical Engineering, Shanghai Jiao Tong Univ., Shanghai, China. His current research interests include ac/dc power system analysis and control, wind and PV power control and integration, and DAB control.

About The Author

Bei Han received M.S degree in electrical engineering from Shanghai Jiao Tong University and received Ph.D degree in electrical engineering from Politecnico di Torino. Currently, she is an Assistant Professor of Shanghai Jiao Tong University. Her research interests are complex distribution system modeling with multi-microgrids and DER uncertainties.

About The Author

Xiuchen Jiang was born in Shandong, China. He received the B.E. degree in high voltage and insulation technology from Shanghai Jiao Tong University, Shanghai, China, in 1987, the M.S. degree in high voltage and insulation technology from Tsinghua University, Beijing, China, in 1992, and the Ph.D. degree in electric power system and automation from Shanghai Jiao Tong University in 2001.

Currently, he is a Professor in the Department of Electrical Engineering, Shanghai Jiao Tong University. His research interests are electrical equipment online monitoring as well as condition-based maintenance and automation.

Reference

Jin Xu, Peter Kairu Kanyingi, Keyou Wang, Guojie Li, Bei Han, and Xiuchen Jiang. Probabilistic small signal stability analysis with large-scale integration of wind power considering dependence. Renewable and Sustainable Energy Reviews, volume 69 (2017), pages 1258–1270.

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Renewable Energy Global Innovations features: Pt monolayer coating on complex network substrate with high catalytic activity

Significance Statement

The demand for platinum has superseded the supply in catalytic applications such as in autocatalytic converters, fuel cells, the petroleum industry among others. This has resulted in platinum being an expensive industrial material and therefore, attempts have been made to fabricate platinum monolayer films and single-atom alloy catalysts. There have been reports on platinum monolayer deposition onto various nanoparticles and single-crystalline surfaces but little has been achieved in the fabrication of complete-monolayer platinum onto a large-piece three-dimensional bulk substrate having a complex geometry.

In a recent research published in Science Advances, Professor Shengzhong (Frank) Liu and coworkers developed an effective method for minimizing platinum usage by synthesizing platinum monolayers onto a large-surface-area three-dimensional nickel foam network by applying a buffer layer method. They have found out that the monolayer is similar to a thick platinum film for catalyzing the hydrogen evolution reaction but it is much much cheaper.

The authors observed that at a negative voltage, there was an increase in current density, which signified the completion of the deposition cycle. This then stabilized indicating the complete termination of the deposition. At zero voltage, the current density initially increased then dropped to zero which showed that there was an immediate desorption of the hydrogen layer to produce a fresh platinum surface.

From further analysis, there was a similar mass gain for every monolayer deposition cycle which meant that each platinum atom had a covalent radius similar to that of platinum. This proved that the coating process is based on the complete-monolayer mechanism. It was also evident that a hydrogen atom forms on top of a platinum atom and as such, the double layer protects the formed platinum surface from any further deposition hence a well-defined platinum monolayer coating is produced.

The researchers also noted that the platinum monolayer applied onto a metal nanofilm and nickel foam functions as a hydrogen evolution reaction catalyst in acidic condition, by lowering the onset potential, which is effective in water splitting. The reduction in overpotential causes increased catalytic activity in the hydrogen evolution reaction.

Further analysis showed that the platinum monolayer-coated catalyst attained catalytic activity that was as high as that of a thick platinum film. This shows that the platinum monolayer completely covered the nickel foam, which means that a complete-monolayer platinum coating is generated onto the large-surface area nickel foam substrate. It is therefore evident from the study that high-activity platinum catalyst can be fabricated with minimal platinum usage thereby minimizing its commercial application costs.

Reference

1. Man Li, Qiang Ma, Wei Zi, Xiaojing Liu, Xuejie Zhu, Shengzhong Liu. Pt monolayer coating on complex network substrate with high catalytic activity for the hydrogen evolution reaction. Science Advances, 2015. Vol. 1, no. 8, e1400268
2. Liuqing Pang, Yunxia Zhang, Shengzhong Liu, Monolayer-by-monolayer growth of platinum films on complex carbon fiber paper structure. Applied Surface Science 2017, 407, 386-390.
3. Liuqing Pang, Man Li, Qiang Ma, Yunxia Zhang, Xianpei Ren, Doudou Zhang, Shengzhong Frank Liu, Controlled Pt Monolayer Fabrication on Complex Carbon Fiber Structures for Superior Catalytic Applications. Electrochim. Acta 2016, 222, 1522-1527.

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Renewable Energy Global Innovations features: 20-mm-Large Single-Crystalline Formamidinium-Perovskite Wafer for Mass Production of Integrated Photodetectors

Significance Statement

Defects such as surface imperfections and grain boundaries within microcrystalline thin films have been the cause of performance killer in perovskite-based devices. Large single-crystalline materials such as methylammonium iodide have been used since they are free from the defects and possess superior characteristics such as ultralow trap state density. Research advancements have shown that the formamidinium lead iodide performs even better as an optoelectronic material with solar cell efficiency greater than 22%. One of the impediments to the advancement of the formamidinium lead iodide is that only smaller single crystalline formamidinium perovskite have been produced and therefore larger wafers and crystals urgently need to be developed.

Shengzhong (Frank) Liu and coworkers applied an inverse temperature reactive crystallization strategy to develop large single crystalline formamidinium perovskite. Their work is reported in Advanced Optical Materials, 2016, 4 (11), 1829-1837;. Advanced Materials, 2016, 28, 9204-9209; Sci. China Chem. 2017, DOI:10.1007/s11426-017-9081-3.

The authors observed that most harvested crystals exhibited rhombic hexagonal dodecahedra shapes with black glossy surfaces. They also noted that a higher relative humidity accelerates color change of the crystal from black to yellow. Thin wafers were prepared using a slicing machine with the thinnest wafer obtained having a 100 µm thickness.

The x-ray diffraction test showed the single crystalline formamidinium perovskite wafer adopts a perovskite structure and that no residue of the reactant precursors is present. Further, from rocking curve measurements it was evident that the wafer exhibits excellent crystalline quality.

From the absorption spectrum of the formamidinium lead iodide there was a cut-off feature indicating that it is a direct bandgap semiconductor, with the absorption edge located at approximately 870 nm, and an optical bandgap of approximately 1.49 electron-volts. The thermogravimetric analysis of the perovskite shows that it is highly stable without any sign of thermal decomposition up to 300 °C as compared with the methylammonium lead iodide perovskite.

The authors established that the trap state density of the as-prepared perovskite was lower than many of the known inorganic semiconductors, and that it has a low carrier concentration with a greater carrier mobility. This affirms that the as-prepared perovskite is of high quality.

The research team also compared photodetectors made of the as-prepared perovskite wafer and a thin film microcrystalline perovskite. They observed that the photocurrent of as-prepared perovskite was about 90 times higher than that of the thin film perovskite, and that it exhibits a significant response in the near-infrared region as compared with the latter, which confirms that the former has a broader optical absorption. The external quantum efficiency, photoresponsivity and response time of the as-prepared perovskite wafer were found to be even greater in the as-prepared perovskite wafer.

Reference

Yucheng Liu, Jiankun Shun, Zhou Yang, Dong Yang, Xiaodong Ren, Hua Xu, Zupei Yang, Shengzhong(Frank) Liu. 20-mm-Large Single-Crystalline Formamidinium-Perovskite Wafer for Mass Production of Integrated Photodetectors. Advanced Optical Materials, 2016, 4, 1829-1837.

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Renewable Energy Global Innovations features: Short-term electric energy production forecasting at wind power plants in pareto-optimality context

Significance Statement

Wind energy is considered as a clean renewable resource that plays an important role in mitigating greenhouse emissions, which are pivotal in climate change. Therefore, there has been observed a consistent growth of the wind energy sector in the recent past. Unfortunately, despite the undoubted features of being a free and clean energy resource, wind power is generally intermittent and uncontrollable. Market participants as well as power system operators therefore face major challenges, one being unable to control uncertainty and variability of wind power generation.

One main duty of transmission system operators is to maintain the balance of electric power generation and electric load. For wind power farms, maintaining the power balance appears to be quite challenging in view of the fluctuating nature of wind resources as well as the problem of large-scale energy storage. Therefore, transmission systems operators generally schedule an optimal combination of controlled generating units to satisfy a forecasted load, while having an assumed wind generation prediction, power system reserve needs and generation and transmission constraints.

Wind power forecasting therefore becomes an indispensable factor for electricity market players, for instance, energy trading companies and wind energy producers. Therefore, Jacek Wasilewski at PSE Innowacje sp. z.o.o and Dariusz Baczynski from the Warsaw University of Technology Poland formulated an approach allowing for estimating an assembly of prediction models satisfying a number of model  learning and testing criteria. They then developed the Pareto-optimization method. They presented a mathematical model and a case study of the wind power-forecasting taking into account the Pareto-optimization of the selected prediction criteria. Their work is published in Renewable and Sustainable Energy Reviews.

The authors discussed and analyzed the application issues of multi-criteria prediction model optimization in the intra- as well as next day wind power prediction. In order to understand the artificial neutral networks, a multi-objective method was developed based on Pareto-optimization. The method takes into account a concept of forecast and enables the analysis of accuracy prediction models implementing a generalized multi-criteria function.

Wasilewski and Baczynski showed that the effectiveness of the ANN-MLP learning reference to a particular criterion could be achieved independently of the algorithms (Back Propagation, Particle Swarm Optimization and hybrid BP+PSO algorithms were used) .The learning process was effective when the learning data set was applied to choose the optimal model.  An excess of coordinate of the utopia vector at the NISE procedure occurred only if the ANN process was not effective. However, the utopia vector was as a result of ANN optimization reference to the testing data.

It was observed that no impact of the analyzed wind farm and the ANN-MLP structure on the given outcomes has been evident in most analyzed situations. The ANN-MLP model was a machine learning model with low bias and high variance. The experiment outcomes presented should be confirmed also with the use of other categories of prediction models and different statistical attributes.

Future works by Wasilewski and Baczynski will perhaps focus on developing an interface between a decision making process and the forecasting. This will be aiming at presenting how operators as well as decision makers in energy markets would implement the proposed forecasting method reference on the multi-criteria approach.

About The Author

Jacek Wasilewski was born in Elblag, Poland in 1981. He received the M.Sc. and Ph.D. degrees in electrical engineering from Warsaw University of Technology in 2005 and 2011 respectively. From 2006 to 2015 he was employed at the Institute of Electrical Power Engineering, Warsaw University of Technology as an academic teacher.

Since 2015 he has been employed at the Research and Development Centre in PSE (Polish transmission system operator) where he is currently a principal consultant.  His interests include methodologies of power system optimisation, both in strategic planning and operation.

About The Author

Dariusz Baczyński was born in Warsaw, Poland in 1972. He received the M.Sc. (1996), Ph.D. (1999) and D.Sc. (2014) degrees in electrical engineering from Warsaw University of Technology. Since 1999 he is an assistant professor at the Institute of Electrical Power Engineering, Electrical Faculty, Warsaw University of Technology. He also cooperated with IT companies as an expert.

His interests include optimisation, forecasting and applications of computer systems in broadly understood electrical power engineering. In particular he is much interested in pareto optimisation and modern computational intelligence methods. As a result of his recent analysis of the latter he developed a new concept of Artificial Ecosystem Algorithm for optimization problems.

Reference

Wasilewski and D. Baczynski. Short-term electric energy production forecasting at wind power plants in pareto-optimality context. Renewable and Sustainable Energy Reviews, volume 69 (2017), pages 177–187.

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Renewable Energy Global Innovations features: Fabrication of air-stable, large-area, PCDTBT:PC70BM polymer solar cell modules using a custom built slot-die coater

Significance Statement

The quest for understanding the operation of polymer solar cells has made it possible for the development of conjugated polymers. This has led to the fabrication of devices with over 10% power conversion efficiency. Longevity stability problems, common for typical polymer solar cells where the cathode is susceptible to water and oxygen degradation, has been curtailed through device structure inversion. Above all, low band gap polymers including PCDTBT have exhibited potential photochemical stability in laboratory and real world operational conditions, posting 7-15 years useful life.

However, production of large-scale polymer solar cells using slot-die coating, inkjet printing, rotary screen-printing, and spray coating methods in the laboratory is less practical considering the high cost of purchase and repeatable operation of the equipment needed. Therefore, most researchers rely on the spin-coating method, which only produces polymer solar cell devices of up to 1cm², and is unsuitable for large-scale production in view of poor material utilization and issues with scaling up. The use of spin coating also creates discrepancies in industrial and research laboratory results owing to significant non-identical effects in the deposition process on device performance.

To address this, researchers led by Professor S. Ravi P. Silva at the University of Surrey described in their work, the adaptation of an entry level paint applicator to function as a functional slot-die coater. This allowed for the attachment of various coating heads for flexible coating. They described the design of slot-die head and its supporting elements. The slot-die coater was then used to produce polymer solar cell modules with over 3% power conversion efficiency determined over 35cm² photoactive area. Their work is published in Solar Energy Materials & Solar Cells.

The authors fabricated polymer solar cell devices with a structure of glass -ITO/ZnO/PCDTBT: PC70BM/MoO3/Al. The electron transport layer solution was then slot-die coated onto the glass indium tin-coated glass substrates. The coating process of the PCDTBT: PC₇₀BM layer was carefully undertaken at ambient conditions on top of the zinc oxide layers.

For modules fabrication, the viscosity of the active layer and subsequently the resulting layer thickness was changed by altering the processing temperature and applying three varying donor acceptor concentrations. The authors made two modules from the first two concentrations and one module from the latter.

The modified sheet-to-sheet slot-die coater was used to produce polymer solar cell modules with an active area above 35cm² and over 3% power conversion efficiency. Optimization of the processing parameters led to homogeneous layers that were characterized by light beam induced current, micro Raman mapping, and micro photoluminescence of the modules. The authors also investigated the behavior of the module at various annealing temperatures as well as its stability during operation, and provide supplementary information on the fabrication of the modified slot die head.

The outcomes of their study provide a route for fabrication of large-scale slot-die coated modules with viable polymer solar cells. This infers that large-scale polymer solar cells can be made with simple coating equipment, therefore, avoiding the high cost of purchase and operation.

The reported work was completed partly in collaboration with European partners through a European Union 7^th Framework Programme (FP7) project entitled Smartonics, and partly in collaboration with the United Kingdom’s national measurement institute, The National Physical Laboratory (NPL). The collaboration with NPL has recently been further supported by a grant from the European Union Horizon 2020 Framework Programme to which will create an effective Open Innovation Environment (OIE) for printed electronics, entitled CORNET, combining world-class expert academic, research and industrial entities from 6 countries, as part of a national metrology effort to standardize printable electronics in an organic electronics market which is predicted to grow to $48B in 2019 (IDTechEx).

Prof Silva indicated that: “Consortia such as the FP7 Smartonics programme have contributed much in setting up a framework to establish printable electronics within the European Union. We hope research such as this, and the recently funded CORNET project, will help firmly establish plastic electronics within the UK and Europe, and provide a resource for researchers worldwide.”

Images produced by Dr Dimitar Kutsarov (ATI, University of Surrey)

About The Author

Professor Ravi Silva is the Director of the University of Surrey’s multi-disciplinary Advanced Technology Institute (ATI, http://ift.tt/2xtEbOq) incorporating over 150 researchers. The ATI is one of University’s world-leading research centres, bringing together researchers with an international outlook in Quantum Information, Nanotechnology, Energy and Advanced Materials.

His research interest encompass a wide range of activities, with nanotechnology and renewables being two underlying themes which thread through a plethora of fields. Within nanotechnology, Ravi is active in carbon nanomaterials (including carbon nanotubes, graphene, diamond like carbon and carbon fibre reinforced plastics), transistor designs & simulations, source gate transistors, nano-biotechnology, large area electronics, and electronic and photonic devices. While within renewables, fields include solar cells, organic photovoltaics, organic light emitting diodes, energy materials for thermo- and tribo-electrics, water technology. In particular, he has an established interest in the development of next generation large area photovoltaics and the production of carbon nanomaterials for advanced manufacturable technologies, as well as the technology required to develop both fields.

The ATI has in particular been recognised for its pioneering work in these fields. For example, Prof. Silva has defined a new generation of materials that is enabling the development of next generation (4G) solar cells. Engineered using nanotechnology, the 4^th generation (4G) solar cell materials are a hybrid of organic and inorganic materials. These devices maximise the harvesting of solar radiation, offering a more efficient, cost-effective solution than existing solar cells. Additionally, researchers at the ATI have used a graphene production technique known as nanotexturing, which involves growing graphene around a textured metallic surface, to create ultra-thin graphene sheets designed to more effectively capture light. Just one atom thick, graphene is very strong but traditionally inefficient at light absorption. To combat this, the team used the nano-patterning to localise light into the narrow spaces between the textured surface structures, enhancing the amount of light absorbed by the material by about 90%, analogous to moths’ eyes which have microscopic patterning that allows them to see in the dimmest conditions.

Ravi passionately believes in developing enabling technologies relevant to major societal challenges, and over 20 years has contributed to the UK knowledge economy in the materials and manufacturing sectors by training more than 50 PhD and 65 postdoctoral staff.

Professor Silva’s work was recently recognised by the award of the IET’s JJ Thomson medal (2014) for major and distinguished contributions in electronics, citing his work on large area [carbon] nanotube-organic solar cells, and the Institute of Materials, Minerals and Mining’s Platinum Medal (2015) for the advancement and promotion of carbon nanomaterials for technology applications.

Reference

Dimitar I. Kutsarov, Edward New, Francesco Bausi, Alina Zoladek-Lemanczyk, Fernando, A. Castro, S. Ravi P. Silva. Fabrication of air-stable, large-area, PCDTBT:PC70BM polymer solar cell modules using a custom built slot-die coater. Solar Energy Materials & Solar Cells, volume 161 (2017), pages 388–396.

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Renewable Energy Global Innovations features: Subcritical carbon dioxide-water hydrolysis of sugarcane bagasse pith for reducing sugars production

Significance Statement

Sugarcane bagasse that is a byproduct of sugarcane extraction process is majorly used in the paper making process. Approximately 40% of this residue is considered small fiber, sugarcane bagasse pith that is eliminated from the pulp for papermaking. Compared to a good number of agricultural residues, sugarcane bagasse pith is also a lignocellulostic material composed of lignin, hemicelluloses and cellulose. A large proportion of this byproduct is normally used for electricity production, but this comes with more carbon dioxide emissions.

Therefore, most researchers have focused on how it can be used for biological fuel production as well as chemicals that can offer economic, strategic, and environmental advantage. Reducing sugars, a biomass precursor that can be changed to fuel alcohol by fermentation, appears to be the best high-added product that can be extracted from sugarcane bagasse pith.

In order to extract reducing sugars from the sugarcane bagasse pith, the hemicelluloses as well as cellulose should be hydrolyzed. Some of the methods for achieving this include, acidic, enzymatic and alkali hydrolysis. Nevertheless, implementing concentrated acids, for instance, hydrochloric and sulfuric acids demands corrosion resistant reactors. Long process time as well as high cost of enzyme production are the major bottlenecks for enzymatic hydrolysis.

Researchers led by professor Xiaopeng Chen from the Department of Chemistry and Chemical Engineering at Guangxi University in China investigated the subcritical carbon dioxide water hydrolysis of sugarcane bagasse pith in the production of reducing sugars. In their study, an orthogonal test method was used to optimize a combination of process parameters, which include stirring speed, reaction temperature, carbon dioxide initial pressure, total reducing sugars, and reaction time. Their work is published in peer-reviewed journal, Bioresource Technology.

The authors carried out the hydrolysis of sugarcane bagasse pith in a stainless steel reactor, which was equipped with a magnetic driven paddle agitator. The reactor was heated and the temperature inside measured and controlled at operating temperature. A magnetic stirrer was then used to continuously mix the content of the reaction.

For carbon dioxide reaction, a stainless steel tube was connected to a valve and fitted to the reactor to allow for controlled introduction of carbon dioxide from a gas cylinder. The initial pressure of the carbon dioxide was then controlled using a high-pressure reactor regulator.

The hydrolysis of the sugarcane bagasse pith to generate reducing sugars under subcritical carbon dioxide-water led to the highest total reducing sugars production of approximately 45.8% at the optimal conditions established by orthogonal design of 200 °C, 1MPa initial carbon dioxide pressure, 40 minutes reaction time, 500rmin^-1 stirring speed, and 50:1 liquid-to-solid ratio.

FT-IR analysis indicated that xylose, arabinose, and glucose were the major components in the hydrolysis liquor. Elementary kinetic processes of biomass solubilisation represented by severity factors could not adequately define the hydrolysis of the sugarcane bagasse pith. Decomposition of the reducing sugars, rate constants, and activation energy of reducing sugar formation were obtained on the first-order kinetic model of consecutive reactions.

About The Author

Professor Xiaopeng Chen’s higher education was at Guangxi University, China. He has been at Guangxi University, China since 1984 progressing to Professor in 2003.

His research activities focus on the Resources Processing and Process Intensification Technology of biomass. He has a special interest in the kinetics and thermodynamics analysis of oleoresin for hydrogenation, dehydrogenation, disproportionation, cracking, and isolation. Professor Chen has published over 200 papers/books/patents in these subjects.

About The Author

Dr. Jiezhen Liang, is a senior experimentalist in the Department of Chemistry and Chemical Engineering at Guangxi University, China. She received Ph.D. degree at the same university in 2017. Her current research focuses on High Efficient Utilization of agriculture waste.

Reference

Jiezhen Liang, Xiaopeng Chen, Linlin Wang, Xiaojie Wei, Huasheng Wang, Songzhou Lu, Yunhua Li. Subcritical carbon dioxide-water hydrolysis of sugarcane bagasse pith for reducing sugars production. Bioresource Technology, volume 228 (2017), pages 147–155.

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Renewable Energy Global Innovations features: Investigation of donor-acceptor copolymer films and their blends with fullerene in the active layers of bulk heterojunction solar cells by Raman micro-spectroscopy

Significance Statement

Low-band gap copolymers as well as their compounds with fullerenes have received a great deal of research attention owing to the fact that they can be used as active layers on organic photovoltaic gadgets. Photovoltaic systems with bulk heterojunctions as well as donor-acceptor blends appear to be the most promising devices.

Photovoltaic gadgets with bulk heterojunctions composed of blends of donor-acceptor copolymers as well as fullerene derivative, phenyl C61-butyric acid methyl ester have shown varying power conversion efficiencies dictated by side chain nature as well as the behavior of the donor units. Blend film quality is an important parameter for photovoltaic device performance. Raman spectroscopy appears as a useful tool for monitoring polymer order, and has enabled the study of chemical composition of blends normally used in bulk-heterojunction structures.

Researchers led by Věra Cimrová from the Academy of Sciences of the Czech Republic studied thin films with three low band gap donor-acceptor copolymers and their blends of varying ratios with the soluble fullerene derivative as heterojunction solar cell layers. They used UV-vis absorption spectroscopy as well as Raman microspectroscopy for the study. In particular, they used Raman measurements with varying excitation wavelengths to differentiate the low-wavelength photoluminescence of the two components in the blends. Their work is published in peer-reviewed journal, Organic Electronics.

 The authors prepared three donor-acceptor copolymers, CDTF, CDTDOP, and CDTDP, composed of 4,6-bis(3′-dodecylthiophen-2′-yl)thieno[3,4-c][1,2,5]thiadiazole-5[Symbol],5[Symbol]-diyl as an electron-acceptor structural unit and electron-donor structural units 9,9-bis(2-ethylhexyl)fluorene-2,7-diyl, 2,5-didodecyloxy-1,4-phenylene and 2,5-didodecyl-1,4-phenylene, respectively. Recent research works of authors have shown that copolymers composed of electron- accepting thienothiadiazole-based components are promising for photovoltaic applications owing to their high electron affinity, low band gap and reversible redox attributes.They prepared polymer and polymers-blend thin films through spin coating onto fused silica substrates from 1,2-dichlorobenzene solutions.

The researchers observed that the maxima of the thin film spectra were red shifted as opposed to the solution spectra indicating strong intermolecular interactions in the solid state. The long-wavelength intra-chain charge transfer absorption of the CDTDOP was observed to be located at lower wavelengths compared to the other two copolymers owing to strong electron donor character of the 2,5-didodecyloxy-1,4-phenylene components as well as stronger aggregation that was also evident in its solution absorption.

The fullerene derivative absorbed in the UV spectral region, and for this reason, in the blend films, the UV absorption was observed to increase with the increase in the fullerene derivative. The absorption in the visible region decreased as compared with the absorption of the thin films. However, there were no shifts observed in the maxima positions of the CDTF and CDTDOP copolymers. This was an indication that blending the copolymers with the fullerene derivative did not hinder planarization of the main chain.

From the Raman spectroscopic studies of the thin films of the three copolymers and their blends with fullerene derivative, the authors observed different behavior in the CDTDP blends from that of CDTF and CDTDOP blends.

The authors found separate regions (in-homogeneities) in the blend films of the copolymers with fullerene. Photoluminescence of the two components determined in the Raman spectra indicated that the in-homogeneities were composed of more fullerene and a small copolymer amount as opposed to homogeneous blend.

The results of their study showed that Raman microscopic and optical absorption approaches are important in getting additional information about polymer molecule planarity as well as interactions in the polymer thin films.

About The Author

Věra Cimrová received her M.Sc. in Biophysics and Chemical Physics (1984) at Faculty of Mathematics and Physics, Charles University in Prague, her Ph.D. in Physical Chemistry (1991) at the Institute of Macromolecular Chemistry (IMC), The Czechoslovak (now Czech) Academy of Sciences, and habilitation in Physics of Molecular and Biological Structures (2013) at Charles University in Prague. In the 1993-1995 and 1998 stayed abroad as a visiting researcher at the Max-Planck-Institute for Polymer Research, in Mainz, Germany. Since 1984 she is working at IMC. Currently she is a head researcher in the IMC (deputy head of Department of polymers for optoelectronics and photonics), and associate professor at Faculty of Mathematics and Physics Charles University in Prague.

She has published more than 100 original papers in impacted international journals and monographs, as well as numerous invited conference lectures and contributions. She was Editor of two Special Issues of Macromolecular Symposia, and also chairperson of 3 international conferences in the series of Prague Meetings on Macromolecules.

Her research interest includes photophysical, electrical, photoelectrical and electrochemical properties of organic materials, polymers and polymer blends, organic photovoltaics and electroluminescence, design and research of new polymers and polymer systems for photonics and electronics.

About The Author

Zuzana Morávková received her M.Sc. in Physics of condensed matter and materials in 2009 and her Ph.D. in 2013 in Polymer physics, both at the Faculty of Mathematics and Physics, Charles University in Prague She is now working as a research associate in the Institute of Macromolecular Chemistry of Czech Academy of Sciences, Department of Vibrational Spectroscopy. She has published 32 papers in impacted journals and 19 conference contributions.

Her research interests cover conducting polymers, related oligomers, and carbon materials, studied by vibrational spectroscopy, microspectroscopy, and spectroelectrochemistry, in various forms such as thin films, colloids, solutions, or composite materials. Within her one year her post-doctoral stay (2015–2016) at the Centre of Spectroelectrochemistry, Leibniz Institute of Solid State and Materials Research, Dresden, Germany, she worked on vibrational spectroelectrochemistry of conducting polymers.

About The Author

Veronika Pokorná received her M.Sc. in Technology of polymer synthesis and processing (1990) at Department of Polymers, University of Chemistry and Technology in Prague and her PhD. in Macromolecular Chemistry (1995) at the Institute of Macromolecular Chemistry, The Czech Academy of Sciences in Prague. She is now working as a research associate in the Institute of Macromolecular Chemistry (Department of polymers for optoelectronics and photonics). She has published 29 papers in reputed reviewed and impacted journals. Her research interest includes syntheses and characterization of polymers.

About The Author

Drahomír Výprachtický received his M.Sc. in Technology of macromolecular materials (1980) and his PhD. in Macromolecular chemistry (1986) at Department of Polymers, University of Chemistry and Technology in Prague. He is now working as head researcher in the Institute of Macromolecular Chemistry, The Czech Academy of Sciences, Prague (Department of polymers for optoelectronics and photonics).

He has published more than 70 papers in reputed impacted journals and more than 100 conference contributions. Within 1991-1997 he spent 5 years as research associate at Polytechnic University, Brooklyn, New York (now NYU).

His research interest includes syntheses and characterization of polymers with fluorescence labels, syntheses of polymers for organic photonics, syntheses of polymer ligands for lanthanides, syntheses of conjugated polymers or application of steady-state and time-resolved fluorescence spectroscopy and nonradiative energy transfer in polymer science.

Reference

Věra Cimrová, Zuzana Morávková, Veronika Pokorná, Drahomír Výprachtický. Investigation of donor-acceptor copolymer films and their blends with fullerene in the active layers of bulk heterojunction solar cells by Raman micro-spectroscopy. Organic Electronics, volume 47 (2017), pages 194-199.

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Renewable Energy Global Innovations features: Alternating precursor layer deposition for highly stable perovskite films towards efficient solar cells using vacuum deposition

Significance Statement

Hybrid organic-inorganic perovskite semiconducting materials developed for field-effect transistors have received a significant research interest owing to their superior optical absorption, tolerances to defects, and charge-carrier diffusion. The power conversion efficiency of these perovskite solar cells have been recorded to rise over the past few years to about 20%. Notwithstanding, fabrication based on the planer architecture has become popular owing to its low fabrication temperature and compatibility with a wide range of substrates.

Unfortunately, incomplete and inhomogeneous coverage of the perovskite films have been identified as the main adversaries limiting device performance. Therefore, there has been extensive research aiming at improving the morphology of the perovskite films by modifying interface layers, precursor solution concentration, and by optimizing annealing time and temperature. Developing new methods for perovskite film deposition such as vacuum deposition and solution deposition have also been explored.

Vacuum processes for thermal co-deposition and sequential deposition of lead chloride and CH₃NH₃I have been focused most, as they are considered efficient for preparing films with excellent uniformity as well as high surface coverage. However, the diffusion of CH₃NH₃I into the vacuum chamber and poor uniformity of the solar cells have limited the number of successful reports implementing vacuum deposition methods.

Researchers led by Professor Shengzhong (Frank) Liu and Dr. Dong Yang from Dalian Institute of Chemical Physics, Chinese Academy of Sciences, achieved a uniform layer-by-layer vacuum deposition by alternating lead chloride and CH₃NH₃I precursor layers. The method allowed the authors to relax the stringent deposition control and monitoring measures, and realized excellent uniformity in film morphology, smoothness, and surface coverage. They recorded a solar cell efficiency of 16.03%, the highest efficiency reported at the time of its publication in peer-reviewed journals, Journal of Materials Chemistry A and Advanced Materials. It is worthwhile to point out that the group has increased the efficiency to as high as 18.34%, remaining their lead in this category.

The authors prepared samples of lead chloride film with different thickness. This was in a bid to investigate the thickness effect of lead chloride layer. They then ensured sufficient amount of CH₃NH₃I and removed the excess amount through post-annealing.

They achieved uniform and full coverage perovskite film when the lead chloride film thickness was smaller than 100nm. When it was more than 100nm, voids appeared in the films because of unreacted lead chloride, and the density and size of the voids increased with the lead chloride film thickness. Therefore, they take turns to deposite 100 nm of lead chloride and then suitable thickness of CH₃NH₃I precursor layers to obtain high quality perovskite films. This proposed method offered very high solar cell efficiency with suppressed performance variation. The power conversion efficiency of these devices implementing the present development reached approximately 16.03%, and the power conversion efficiency of the large active area device reaches 13.87%.

The method proposed in this study comes with a number of advantages. First, it relaxes the complicated operations concerning deposition rates control and monitoring. It provides high quality perovskite films with smaller roughness, uniform morphology, full surface coverage, and crystalline phases of higher purity. The controlled deposition environment makes possible the manufacture of dense and pure perovskite films, which results in efficient moisture protection yielding excellent device stability.

The proposed method in the study provided an efficient approach for the fabrication of large area perovskite solar cells. It appears promising for application in the manufacture of large area perovskite solar cells.

Reference

Dong Yang, Zhou Yang, Wei Qin, Yuliang Zhang, Shengzhong (Frank) Liu and Can Li. Alternating precursor layer deposition for highly stable perovskite films towards efficient solar cells using vacuum deposition. J. Mater. Chem. A, 2015, 3, 9401–9405.

Yang; R. Yang; X. Ren; X. Zhu; Z. Yang; C. Li; S. F. Liu, Hysteresis-Suppressed High-Efficiency Flexible Perovskite Solar Cells Using Solid-State Ionic-Liquids for Effective Electron Transport. Adv Mater 2016, 28 (26), 5206-13.

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Renewable Energy Global Innovations features: The illumination angle dependency of CPV solar cell electrical performance

Significance Statement

Concentrated photovoltaics systems are designed to give electrical power at a lower cost than traditional photovoltaics. In order to achieve this, excellent performance from the multi-junction solar cells optimized for concentrators must be achieved, while minimizing the cost of optics, temperature control and other system balances.

Variance in incidence angles of light at the solar cells surface is a particular attribute of the lens-based concentrated photovoltaics. In addition, there has been a concern of inhomogeneity of the light distribution on the cell. These are some of the causes for low performance owing to an increase in series resistance and current mismatch between junctions. For this reason, most concentrators have been designed with an aim of minimizing the inhomogeneity by homogenizing secondary optical element.

Secondary Optical system reduces spatial as well as spectral inhomogeneity through several internal reflections of the incident light. A secondary optical system also adds secondary concentrations to a concentrated photovoltaic system. Unfortunately, as the performance is enhanced and the irradiance homogenized the average incident angle on the surface of the cell increases further. Therefore, concentrated photovoltaic cells in conjunction with a secondary optical system will experience a loss in performance by the angle of incidence variance caused by the optics.

Leon Bunthof and co-workers at Radboud University in The Netherlands studied in detail the effect of oblique illumination of concentrated photovoltaic solar cells performance. Previous studies on this angular dependence have been pegged to the optical coupling difference between junctions as a function of incident angle as well as temperature. In the current study, they focused on the total electrical output of concentrated photovoltaic solar cells as a function of the incident angle. Their work is published in Solar Energy.

The authors used solar cells equipped with an Anti-Reflection Coating for use with secondary optical system as well as front contact metal tabs, similar to solar cells typically applied in concentrator systems. The cell featured a silver front grid contact with fingers with inclined sides.

For uncoated cells, the transmittance of incident photons to the semiconductor element was dependent on the angle of incidence. Therefore, a cell equipped with anti-reflection coating were expected to have a different transmission curve, but these cells also indicated increased reflections at oblique angle of incidence.

The researchers observed that the solar cells performed considerable worse as the illumination became more oblique. For an angle of incidence of 83°, they recorded a drop in performance of  up to 58%. This drop in the performance of the cell was referenced to the optical attributes of the anti-reflection coating considering that the computed angle of incidence dependent transmission through the coating correlated well with the observed angle of incidence dependent cell performance.

The second loss mechanism was found and referenced to the front contact grid by propagating the angle of incidence orthogonal to the grid fingers. For this case, an increasing illumination fraction interacted with the sides of the grid metal for increasing angle of incidence. Therefore, shape and orientation of the grid fingers became a critical source of cell performance loss for the oblique illumination. Additional 18% loss in current generation could then be attributed to front grid.

In order to determine the sensibility of application of a secondary optic element, the optical performance of several model secondary optics was evaluated by ray tracing simulations. The concentrating elements showed a clear increase in optical performance, that leads to a gain in electrical solar cell parameters, in these cases exceeding the loss caused by the elevated illumination angle.

The authors concluded from their study that grid orientation and design with respect to the optical system should be considered and optimized carefully using methods as described in the article, when designing concentrated photovoltaic systems.

Author comment:

In recent years the field of building-integrated photovoltaics has seen a tremendous growth. Concentrator systems especially, offer great benefits when incorporated in a building, as they allow the possibility for multi-functionality in the form of e.g. the direct use of heat, or the regulation of daylight entering the building interior. However the building incorporation puts design constraints (e.g. size, weight) on the concentrating solar systems, which therefore often feature much more complex optical systems than applied in conventional concentrators. This leads to stronger inhomogeneity in cell illumination profile, and a further elevated cell illumination angle. In designing such systems especially, it is of great importance to consider the function of each system component carefully, using experimental measurements, or ray tracing.

About The Author

Leon Bunthof received his Master’s degree in chemistry from Radboud University (Nijmegen, The Netherlands) and is currently a PhD candidate at the Applied Materials Science department of that university.

His research mainly focuses on high-efficiency multi-junction solar cell performance under various types of inhomogeneous illumination patterns.

Such inhomogeneity occurs in concentrator photovoltaic applications, because of the focusing nature of the optics and the wavelength dependent refraction of light. In building integrated systems especially, the inhomogeneity can be strong, because of the more complex optics applied.

About The Author

Joep Bos-Coenraad is currently the CEO of LocalGames, a company that develops adventure games for social or commercial purposes. After receiving his Master’s degree in chemistry and software engineering from Radboud University (Nijmegen, The Netherlands), he has worked at their department of Applied Materials Science focusing on solar concentrators.

There he developed the freely available ray tracer ‘Scientrace’ that is a powerful tool in solar cell and optics research.

Reference

L.A.A. Bunthof, J. Bos-Coenraad, W.H.M. Corbeek, E. Vlieg, J.J. Schermer. The illumination angle dependency of CPV solar cell electrical performance. Solar Energy, volume 144 (2017), pages 166–174.

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Renewable Energy Global Innovations features: Solid-binding peptides for immobilization of thermostable enzymes to hydrolyze biomass polysaccharides

Significance Statement

Immobilization of enzymes onto solid supports can be achieved by a number of physical and chemical methods including, covalent attachment, adsorption, crosslinking and encapsulation. Immobilized enzymes, as opposed to soluble enzymes, offer better stability and easier removal from reaction mixtures, enabling repetitive use in batch and continuous bioprocesses and rapid termination of reactions.

Unfortunately, typical enzyme immobilization approaches usually result in a non-uniform orientation of the enzyme as well as unwanted conformational changes that alter their active sites and may curtail the catalytic activity of the enzyme. Solid-binding peptides have binding affinity as well as selectivity to the surfaces of solid materials such as glass, polymers, silica, metals and zeolite, all support materials employed with biocatalysts.

Solid-binding peptides typically are used as molecular linkers for functional protein immobilization onto solid surfaces without the need for any chemical reactions or even physical treatments.

Researchers led by Professor Anwar Sunna at Macquarie University in Australia have presented the implementation of the solid-binding peptide-mediated immobilization of industrially-based enzymes onto a low cost solid zeolite matrix. The introduction of crosslinking of the immobilized enzymes to create single as well as multiple enzyme biocatalytic modules enabled the authors to highlight the feasibility of this technology for its integration in industrial-scale processes. Their work is published in Biotechnology for Biofuels.

The research team genetically fused the silica-binding linker peptide to three thermostable polysaccharide-degrading enzymes for potential application in industrial-scale biocatalysis. The linker had significant affinity for silica-containing supports allowing for directional immobilization of these enzymes onto the zeolite matrix. The enzymes were observed to retain their binding affinity for zeolite and their biological activity. The integration of the linker did not have adverse effects on the pH and temperature optima of the polysaccharide-degrading enzymes and the assembled single and multiple enzyme biocatalytic modules retained their specific hydrolytic activities upon several rounds of recycling at high temperatures.

Professor Sunna summarized the importance of this platform technology saying; “Despite the promising characteristics of solid-binding peptides, their practical application has been mostly in nanobiotechnology, where immobilization of biomolecules generally relies on exotic and expensive laboratory-based matrices that may not be realistic economically for large-scale processes. Inorganic bulk materials like zeolite and silica are excellent carriers due to their structural and operational stability and their lack of susceptibility to microbial degradation. The combination of solid-binding ability and low-cost bulk materials represents an ideal technology for production of industrial-scale biocatalysts.”

The linker system developed in their study minimizes the time wasted in choosing precipitants as well as crosslinking reagents. Its compositional and structural characteristics allows it to impart orientation and directionality to enzymes after crosslinking. This combination results in improved enzyme reusability. Therefore, this linker technology presents an inexpensive immobilization approach for industrially based enzymes.

About The Author

Andrew Care is a Research Fellow in the ARC Centre of Excellence for Nanoscale BioPhotonics, a transdisciplinary research centre that aims to develop innovative nanotechnologies to investigate complex living systems. He obtained his PhD from Macquarie University in Sydney, Australia.

His current research is focused on the use of solid-binding peptides to control the immobilization of proteins and enzymes onto solid matrices in a range of biotechnological applications, including biocatalysis.

About The Author

Kerstin Petroll obtained her Diploma degree in Food Chemistry at the Karlsruhe Institute of Technology (KIT) in Germany. She was awarded a Macquarie University Research Excellence Scholarship to join Macquarie University as a postgraduate student in 2015. Initially, she focused on analytical sciences of plant metabolites and proteins for medical applications before changing to the field of synthetic biology with a focus on environmental applications. Her PhD project aims at the assembly of a cell-free synthetic pathway to produce a platform chemical from renewable low-value compounds.

About The Author

Peter Bergquist is Emeritus Professor in the Biomolecular Discovery and Design Research Centre at Macquarie University. He has a PhD and DSc from the University of Auckland in New Zealand and has been a Postdoctoral Fellow and Research Fellow at Harvard Medical School, Yale and Oxford Universities and a Visiting Fellow at New York University School of Medicine.

He is one of the pioneers of cloning and expressing genes from extremely thermophilic bacteria. He has an interest in biofuels that stems from early studies of cellulolytic microorganisms and their enzymes for biomass breakdown. He has been on the editorial boards of several significant journals such as Applied and Environmental Microbiology and Journal of Bacteriology.

About The Author

Anwar Sunna is an Associate Professor in Synthetic Biology in the Department of Chemistry and Biomolecular Sciences at Macquarie University (MQ), Sydney, Australia. He obtained a PhD from the Hamburg University of Technology in Germany. He was manager of the Environmental Biotechnology Co-operative Research Centre at MQ and later was the recipient of the prestigious Vice-Chancellor’s Innovation Fellowship.

His recent research has been on the interaction between biomolecules and inorganic compounds including new synthetic peptide linkers with applications in enzyme immobilisation and functionalisation of nanomaterials. Anwar is a member of the MQ Biomolecular Discovery and Design Research Centre, MQ Biosecurity Futures Research Centre, Australian Research Council (ARC) Training Centre for Molecular Technology in the Food Industry and the ARC Centre of Excellence for Nanoscale BioPhotonics. He is also one of the directors of Synthetic Biology Australasia.

Reference

Andrew Care, Kerstin Petroll, Emily S. Y. Gibson, Peter L. Bergquist, and Anwar Sunna. Solid-binding peptides for immobilization of thermostable enzymes to hydrolyze biomass polysaccharides. Biotechnol Biofuels (2017) 10:29.

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Renewable Energy Global Innovations features: Graphene oxide/WS2/Mg-doped ZnO nanocomposites for solar-light catalytic and anti-bacterial applications

Significance Statement

Semiconductor oxides find an array of applications in water purification for photocatalytic degradation of organic dyes. Zinc oxide is perhaps the most popular component for photocatalytic applications owing to its wide band gap, low cost, environmental friendliness, and large exciton binding energy leading to superior optical activity. This makes zinc oxide an important ingredient for photo catalyst for organic pollutants treatments.

However, high recombination rate of electron-hole pairs in semiconductors as well as insufficient solar spectrum absorption limit its photocatalytic reaction efficiency. Doping, constructing heterojunctions and catalyzer carrier are viewed as solutions to these problems, and are used mainly to enhance the photocatalytic activity of zinc oxide nanostructure. Doping the zinc oxide with a suitable element is an important approach for improving its sunlight absorption.

Catalyzer carrier is viewed as an effective approach for decreasing recombination rate of photo generated electron-hole pairs. Graphene is an important catalyst support, which has been deemed as the most promising building block to trap and transfer the photo-induced electrons because of its large surface area, high carrier capacity, and large electronic storage ability. Graphene can fix zinc oxide nanoparticles defects for conducting electron and function as a conducting network. It can as well prevent zinc oxide from aggregation and result in the improvement of the photocatalytic performance.

A group of researchers led by Professor Yuenhong Tsang at The Hong Kong Polytechnic University Shenzhen Research Institute demonstrated the scalable approach to fabricate large amount of tungsten disulfide Nano plates through the mechanical shear exfoliation approach. They adopted a versatile method to produce 3D reduced graphene oxide-tungsten disulfide nanosheet magnesium doped zinc oxide hybrid implementing a layer-by-layer assembly method. They achieved photocatalytic attributes enhancement adopting the 3D graphene tungsten disulfide hybrid. Their work is published in Solar Energy Materials & Solar Cells.

The authors used Rhodamine as a model dye in a bid to evaluate the photocatalytic activity of the specimens. The research team computed the degradation ratio as the quotient between original concentration and the residual concentration at varying time. After a complete degradation of the Rhodamine, the authors isolated the graphene nanocomposites and added them to a different solution with the same Rhodamine concentration. This was in a bid to analyze the photocatalytic stability of the resulting composites.

The authors observed the adsorption ability of the specimen before opening light in order to differentiate adsorption effect and photocatalytic ability of the samples for Rhodamine. They realized that the adsorption ratio of all samples for Rhodamine was less than 10% in the dark. When exposed to about 100W UV light irradiation, the group without a photo catalyst indicated about 20% photo degradation. However, a 60% photo degradation was recorded when reduced graphene oxide/magnesium doped zinc oxide composites samples were imported.

However, a 90% removed rate of reduced graphene oxide-tungsten disulfide nanosheet magnesium doped zinc oxide hybrid for Rhodamine was recorded after 5 min, and the Rhodeamine was completely removed after 10min.

Inhibition rings sizes against E, coli as well as S. aureus were 8.64mm and 6.07mm respectively for magnesium doped zinc oxide specimen.  However, when graphene was introduced, the rings sizes increased to 9.23mm and 10.21mm.

Tungsten disulfide nanosheet played a critical role in improving photocatalytic and antibacterial activity of the magnesium-doped zinc oxide composite. The outcomes of the study prove that the resulting 3-D tungsten doped zinc oxide composites could be good candidates for sunlight-driven photocatalytic, self-cleaning, environmental protecting, and photovoltaic applications.

About The Author

Dr. Yuen Hong Tsang has completed his undergraduate and PhD study in the School of Physics and Astronomy, The University of Manchester, UK in 2004. He came back to Hong Kong in 2009 and he is now Assistant Professor in Applied Physics Department, The Hong Kong Polytechnic University. He has published >100 SCI international peer reviewed journals with H-index >20 and total citation >1400.

His current research interests include development of novel materials, e.g. graphene, MoS₂, WS₂ etc. for laser photonics, photo-catalysis, solar energy conversion applications, e.g. photo-catalyst, solar heat absorber, saturable absorber, optical limiter, photo detection, fiber laser, Q-switched and mode locked lasers, etc. He has involved and successfully completed several research projects funded by some well-known international companies.

These projects include 1.  Laser range funder for military applications (funded by Thales.) 2. Imaging system for dental applications (funded by Colgate Palmolive) 3. Narrow linewidth tunable lasers (funded by Huawei) 4. Carbon based mode locking laser system (funded by Fianium Asian Ltd.)

Reference

Chuansheng Chen, Weiwei Yu, Tiangui Liu, Shiyi Cao, Yuenhong Tsang. Graphene oxide/WS2/Mg-doped ZnO nanocomposites for solar-light catalytic and anti-bacterial applications. Solar Energy Materials & Solar Cells, volume 160 (2017), pages 43–53.

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Renewable Energy Global Innovations features: Enhanced lifetime of organic photovoltaic diodes utilizing a ternary blend including an insulating polymer

Significance Statement

Organic photovoltaic diodes appear to be a promising technology because of their potential use in synthesizing low-cost, flexible, large area and lightweight electronics. Unfortunately, the limited lifetime of organic photovoltaic diodes hinders their commercialization. For example, a thousand hours lifetime reported for poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester solar cells is inferior to that of silicon photovoltaics whose lifetime extends up to 25 years.

The degradation of these solar cells remains a limitation and many researchers are still looking for ways to improve their performance. Organic photovoltaic diodes degrade owing to chemical and physical processes. Chemical degradation results from oxygen, light, water and temperature. However, water and oxygen are considered the principle factors; these oxidize the organic photovoltaic materials as well as electrodes leading to poor performance and electronic traps.  Degradation may also result from the bulk heterojunction morphology since the constituent materials may aggregate with time, leading to reduced exciton dissociation and poor performance.

Blending the active semiconductor with an inert polymer appears to improve the lifetime of the organic photovoltaic diodes. A team of researchers under the guidance of Professors Chris Groves and Michael Petty at Durham University in United Kingdom investigated the use of an insulating polymer, poly(methyl methacrylate), as a ternary component in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester solar cells as a way of enhancing their lifetime and reducing degradation. Their research work is now published in Solar Energy Materials & Solar Cells.

The authors separately prepared poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester solutions before mixing in a 1:1 weight ratio. In a bid to make the ternary blend, they first prepared poly(methyl methacrylate) solution by dissolving in anhydrous 1,2-dichlorobenzene to obtain a clear solution.

The authors stirred both the ternary and binary organic photovoltaic blends before spin coating them onto the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). They annealed all devices before lifetime tests.

The research team observed that the addition of poly(methyl methacrylate) improved both the initial performance as well as the lifetime of the solar cells. Measurement of the different relative humidity values suggested that poly(methyl methacrylate) absorbed water, thereby reducing the rate of chemical degradation in the solar cell. The lifetime improvement with poly(methyl methacrylate) reduced with decreasing humidity. This suggested that the poly(methyl methacrylate) becomes saturated. A number of studies revealed that the addition of poly(methyl methacrylate) led to a morphology containing poly(methyl methacrylate) pillars dissimilar to the morphology seen in the binary film.

Electrical conductivity did not degrade at different rates across the ternary film. This suggested that water diffused microns through the film before reacting with the active material. The rate of conductivity degradation was similar for binary and ternary devices. This indicated that various degradation mechanism were present, and that poly(methyl methacrylate) only assisted in extending the lifetime associated with a selected degradation pathways.

Power conversion efficiency of the poly(3-hexylthiophene): phenyl-C61-butyric acid methyl ester solar cells is severely limited by reaction with water. The incorporation poly(methyl methacrylate) slows down this degradation process through water absorption. The results of their study suggest that electrically inert and hydroscopic polymers can be blended with an organic photovoltaic active layer to extend the device lifespan.

The addition of PMMA to a P3HT:PCBM solar cell slows down the device degradation. Left: Power conversion efficiency (PCE) as a function of time for binary P3HT:PCBM (1:1) blend and ternary (1:1:0.3) P3HT:PCBM:PMMA blend solar cells, stored at a relative humidity (RH) level of 1%. Right: AFM topography image of as-deposited (1:1:0.3) ternary P3HT:PCBM:PMMA blend film. The PMMA is in the form of circular islands.

About The Author

Mrs Zakiya AL-Busaidi received her M.Sc. degree in physics at Sultan Qaboos University, Oman.  She is currently a PhD student in the School of Engineering and Computing Sciences, Durham University, UK. Her current research focuses on how to enhance the lifetime of organic photovoltaics by using insulating polymers.

About The Author

Dr Chris Groves is an Associate Professor at the School of Engineering and Computing Sciences at Durham University, UK, where he is also a Director of the Durham Centre for Molecular and Nanoscale Electronics. He completed his PhD on III-V photodetectors at Sheffield University in 2004, before undertaking postdoctoral positions in the field of organic electronics at the Cavendish Laboratory and the University of Washington.

His research interests focus on the use of experiment and simulation to examine the relationship between charge transport and the performance of electronic devices. Recently, this has involved the development of Monte Carlo models and experimental techniques to reveal how morphology influences charge transport, and ultimately performance, in organic photovoltaic diodes.

About The Author

Dr Christopher Pearson received the Degree in Physical Electronics from Newcastle Polytechnic, Newcastle, UK, and a PhD, focusing on thin films of organic charge-transfer materials, from Durham University, Durham, UK, in 1997. Since 1981, he has been working at the University of Durham. Currently, he is an Experimental Officer with the Durham Centre for Molecular and Nanoscale Electronics, providing support for the group and carrying out research on organic thin films prepared using a variety of techniques.

About The Author

Professor Michael Petty’s higher education was at Sussex University, UK (BSc and DSc) and Imperial College, London (PhD Electronic Materials.) He has been at Durham University, UK since 1976 progressing to Professor in 1994, then Chairman of the School of Engineering from 1997 to 2000.

His research activities focus on the properties of thin films of organic materials (Langmuir-Blodgett, self-assembled, electrostatically deposited, evaporated). He has a special interest in the application of these layers to electronic and opto-electronic devices. Professor Petty has lectured extensively worldwide and published over 400 papers/books/patents in these subjects.

He is a member of Durham University Centre for Molecular and Nanoscale Electronics

Reference

Zakiya AL-Busaidi, Christopher Pearson, Christopher Groves, Michael C. Petty. Enhanced lifetime of organic photovoltaic diodes utilizing a ternary blend including an insulating polymer. Solar Energy Materials & Solar Cells, volume 160 (2017), pages 101–106.

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