Renewable Energy Global Innovations features: Increased short-circuit current density and external quantum efficiency of silicon and dye sensitised solar cells through plasmonic luminescent down-shifting layers

Significance Statement

Luminescent down-shifting is an optical approach to increase photovoltaic device efficiency and it consists of luminescent species such as quantum dots, organic dies and rare-earth complexes doped in a transport polymer sheet and deposited on top of photovoltaic cells.

Spraying of luminescent species on top of photovoltaic cells either by spray coating or incorporation into a multifunctional coating system based on photo-curable fluoropolymer have shown significant improvement in power conversion efficiency of uncoated dye sensitized solar cells devices thereby improving cell stability and prevention of photochemical and physical degradation.

In a recent article by Ahmed et al. (2016) and published in Solar Energy, investigations were made on plasmonic luminescent down-shifting (pLDS) layers applied to silicon cells (c-Si) and dye sensitized solar cells (DSSC) solar cells.

Quantum dots exhibits broad absorption spectra, high absorption coefficients and emission wavelength which can be tuned according to their size as a result of quantum confinement having advantages over organic dies due to their higher brightness and stability. However, the luminescent down-shifting suffer from self-absorption; a case where downshifted photons are reabsorbed by quantum dots or dye within the downshifting layer. Optical properties of luminescent species according to research were shown to exhibit dramatic emission enhancement in presence of metal nanoparticles on quantum dots ion dye emitters.

For the experiments, core-shell type Cadmium Selenide/Zinc Sulfide (CdSe/ZnS) quantum dots were used as fluorescent material which has a quantum yield of 0.7±0.07 measured in solution. Silver nanoparticles were used in plasmonic luminescent down-shifting composite layer and preparation of fluorescent species with silver nanoparticles composite layers followed.

The performance of c-Si and DSSC solar cells encapsulated with quantum dots luminescent down-shifting layer and plasmonic-quantum dots luminescent down-shifting composite layer was compared.

Absorption and emission measurement of quantum dots with/without silver nanoparticles revealed significant increase in emission for the plasmonic luminescent down-shifting layer when compared to layer with no silver nanoparticles. This result shows enhancement attributed to silver nanoparticles exhibiting strong scattering of incident light which greatly enhances local electric fields at surface plasmon resonance frequency.

Current-voltage curves for c-Si and DSSC solar cells showed electrical characterization increase of 1.92% in current density due to presence of quantum dots when compared to bare c-Si cells. Enhancement of 7.84% was calculated for plasmonic-quantum dots luminescent down shifting composite layer. There was also 5.81% increase in current density for plasmonic-quantum dots luminescent down shifting composite layer when compared with quantum dots luminescent down shifting layer.

Electrical characterization of DSSC solar cells showed a decrease of 8.03% in current density of quantum dots luminescent down shifting when compared to bare DSSC solar cells while enhancement of 3.31% was calculated for plasmonic-quantum dots luminescent down-shifting composite layer. There was also 11.29% increase in current density for plasmonic-quantum dots luminescent down shifting composite layer when compared with quantum dots luminescent down shifting layer.

External quantum efficiency of bare c-Si solar cells was poor reaching only 11% at wavelength below 400nm. Improvement of external quantum efficiency at the same wavelength for quantum dots luminescent down-shifting layer and plasmonic-quantum dots luminescent down-shifting layer were 23% and 52%, respectively. The high improvement in plasmonic-quantum dots luminescent down-shifting layer can be attributed to presence of silver nanoparticles in its composite layer.

The external quantum efficiency of DSSC solar cells had overall decrease between 300-800 nm for quantum dots luminescent downshifting layer. However, plasmonic-quantum dots composite layer show 3.03% increase when compared to DSSC bare solar cell and 11.71% when compared to quantum dots luminescent down-shifting device. Significant increase was calculated between 300 and 500nm where current density J_sc reached 21.64% and 5.16% for plasmonic-quantum dots composite layers compared to bare DSSC solar cell and quantum dots luminescent down-shifting device, respectively.

 CdSe/ZnS quantum dots investigations in Ahmed et al. (2016) studies has the ability to absorb light below 465nm and emits at 500nm flows shifting the optical wavelength of the cell from poor optical response (short wavelengths) to external quantum efficiency (at longer wavelengths).

The research team for the first time demonstrated plasmonic luminescent down-shifting current density J_sc reaching up to 22% increase in region of 300-500nm for c-Si and DSSC solar cells.

About The Author

Dr. Hind Ahmed is a graduate of the prestigious Graduate Studies Program at the Singularity University, NASA AMES, California, USA. She has a strong background in Mathematics, Physics and Engineering with the focus in the area of solar energy research. She holds an Honour’s degree in Physics, a Postgraduate Diploma in Mathematical Sciences, a Master degree in Material Physics, a Professional Master in Micro/Nano Electromechanical System and a PhD in Physics.

She is currently working as post-doctoral researcher in the Solar Energy Applications group in Trinity College Dublin under ERC Starter grant (PEDAL) which involves the design, development, characterization and fabrication of large scale plasmonic luminescent down shifting devices for enhancing the efficiency of solar cells. 

About The Author

Dr. John Doran

Affiliation: School of Physics, Dublin Institute of Technology (DIT), Ireland

Professional Appointments:

Head of School, School of Physics, DIT: 2009-present

Assistant Head of School, School of Physics, DIT: 2003 – 2009

Lecturer, School of Physics, DIT: 1996 – 2003

Postdoctoral Research Fellow, School of Physics, TCD, 1994 – 1996.

Education: BA(Mod) Experimental Physics, 1989, Trinity College Dublin

PhD, 1994, Trinity College Dublin – Thesis Title: Exciton Dynamics in CdZnTe/ZnTe Multiple Quantum Wells.

Research and Professional Experience:

Solar Energy Group within the Dublin Energy Lab. Research involves two aspects: 1. Design, fabrication, optical and electrical characterisation, and modelling of Luminescent Solar Concentrators (LSCs) and Luminescent Downshifting (LDS) devices incorporating plasmonic effects.

Applications of switchable mirror technology to solar energy. Recent research has focused on the novel incorporation of metal nanoparticles into LSC and LDS devices in order to enhance optical emission and overcome losses inherent in these devices. This novel plasmonic approach has been demonstrated experimentally and device performance has been modelled successfully using a ray-tracing approach. 

About The Author

Dr Sarah McCormack is an Associate Professor and lead PI in the Solar Energy Applications group in Trinity College Dublin. She has been working in the area of solar energy research for over 15 years. She has published over 90 publications in the areas of solar energy and energy storage and has over 1000 citations. She has supervised 11 PhD students to completion and is currently supervising a further 6 along with 4 Post doctoral researchers. She has been awarded funding of over 3M in national and EU funded projects. She is the Irish representative on European PV Technology Platform Mirror Group nominated by the Sustainable Energy Authority of Ireland, a member of the Renewable Heating and Cooling Platform, Secretary of the Solar Energy Society of Ireland. Recently she has been awarded a prestigious ERC Starter grant (PEDAL) to continue her work in LS devices for enhancing the efficiency of solar cells. 

Journal Reference

Ahmed H¹, Doran J², McCormack S¹. Increased Short-Circuit Current Density and External Quantum Efficiency of Silicon and Dye-Sensitized Solar Cells through Plasmonic Luminescent Down-Shifting Layers.  Solar Energy, Volume 126, 2016, Pages 146–155.

Show Affiliations

1. School of Engineering, Trinity College Dublin, Dublin, Ireland
2. Dublin Energy Lab, Dublin Institute of Technology, Dublin, Ireland

 

 

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