Renewable Energy Global Innovations features: Panchromatic copper(I)-based dyesensitized solar cells

Significance Statement

The use of  n-type dye sensitized solar cells for the conversion of solar photons into electrical energy is now a mature field of research with the conversion efficiency extending beyond 11% to approximately 14%. This has been made possible by the implementation of ruthenium-based, zinc(II), and organic porphyrin-based dyes. Unfortunately, the low earth abundance and high cost of ruthenium-based sensitizers have continued to limit their application despite them taking the lead among inorganic compounds. However, copper-based dyes are sustainable and appear to be promising alternatives to ruthenium.

In order to achieve high performance of dye-sensitized solar cells, the absorbance of the incident rays, injection of electrons into the semiconductor, and the interconnection between the electrolyte and the dye must be optimal. When the absorption range of the dye overlaps with the spectrum of the incident rays, there is a possibility of attaining higher conversion efficiencies. It has been observed that the most efficient copper-based dyes attain >3% photoconversion efficiency, which is relative to the values in the range of 7.12-7.63% for the benchmark ruthenium dyes.

Contrary to the panchromatic absorption of ruthenium dye N719 as well as related dyes, the metal-to-ligand charge transfer band of copper(I) sensitizers is typically in the range of 430 to 570 nm. However, this range can be extended by broadening the π-system of the copper-bound ligands. This would result in higher short-circuit current density values, but would not necessarily lead to enhanced global efficiency.

Frederik Malzner, Markus Willgert, Edwin Constable and Catherine Housecroft at the University of Basel in Switzerland successfully reported the first co-sensitization of a copper(I)-based dye-sensitized solar cell with a complementary organic dye in a bid to realize improved dye-sensitized solar cell photo-conversion efficiency. Their research work is published in Journal of Materials Chemistry A.

The authors described the first example of co-sensitization in dye-sensitized solar cells implementing copper(I)-based sensitizer as well as a commercially available dye. The authors combined the heteroleptic copper(I) dye with a commercially available squaraine derivative. They then matched the external quantum efficiency maxima from the two dyes in complementary parts of the visible spectrum.

Through this combination, the authors realized the highest photo-conversion efficiency of 65.6% so far reported for a copper-based dye-sensitized solar cell. This is the confirmation of the potential implementation of earth-sustainable copper as a sensitizer in dye-sensitized solar cells.

The Swiss research team found that the sequences in which the photo-anodes of the n-type dye-sensitized solar cells were exposed to the heteroleptic copper(I) dye and the squaraine derivative, as well as the time the electrodes were exposed to the dyes, immensely affected the overall performance of the solar cells. The aggregation of the squaraine molecules on the surface of the electrode was necessary for realizing panchromatic light harvesting for the co-sensitized dye-sensitized solar cells. However, excess aggregation would have been detrimental. The outcomes of the external quantum efficiency measurements done with varying wavelength-range filters were consistent with the two dyes operating separately.

About the author

Frederik J. Malzner is currently working towards his PhD in the Constable/Housecroft Research Group at the University of Basel, Switzerland. He received his MSc in Chemistry at the same University in 2014. His research focuses on the investigation of copper(I)-based dye-sensitized solar cells, in particular, optimization of ancillary ligands and co-sensitization with organic dyes with the ultimate goal of achieving panchromatic light-harvesting and enhanced photoconversion efficiencies. His interests in dye-sensitized solar cells have continued throughout both his MSc and PhD studies.

About the author

Markus Willgert held a post-doctoral position in the Constable/Housecroft Research Group at the University of Basel. His research emphasis was on quasi solid and gel nano-crystalline cellulose electrolytes for dye-sensitized solar cells, and he was also involved in work on cobalt electrolytes and p-type cells. He acquired a PhD in fibre and polymer science, regarding solid ion conductors for structural battery applications, at The Royal Institute of Technology in Stockholm, Sweden, where he also received his MSc. His MSc diploma work was carried out at the University of Massachusetts, Amherst, focusing on surface modified, electrically conductive cellulose.

About the author

Catherine E. Housecroft is Professor of Chemistry at the University of Basel. She is co-director of a highly active research group with Edwin Constable and has a broad range of interests spanning structural, organometallic, coordination and materials chemistries.

Current research focuses on the applications of coordination chemistry to sustainable energy (including dye-sensitized solar cells), functional coordination polymers and the hierarchical assembly of surface-anchored functional molecules. She has published over 500 research papers and review articles and is also an internationally recognized author of chemistry textbooks.

About the author

Edwin (Ed) Constable is Professor of Chemistry at the University of Basel and has been involved in supramolecular chemistry since its inception. He has published over 600 research papers and reviews. His scientific interests and expertise lie in metallosupramolecular and materials chemistry, especially in the use of metal ions for the assembly of novel architectures incorporating specific electronic or photophysical properties. Particular emphasis lies upon the development of new sustainable materials chemistry for the dye-sensitized nano crystalline solar cell and OLEDs and related lighting technologies. He received an ERC Advanced Grant (2011-2016) for his project LiLo (Light-In, Light-Out) relating to sustainable materials chemistry.

Reference

Frederik J. Malzner, Markus Willgert, Edwin C. Constable and Catherine E. Housecroft. The way to panchromatic copper(I)-based dyesensitized solar cells: co-sensitization with the organic dye SQ2. Journal of Materials Chemistry A, volume 5 (2017), pages 13717–13729.

 

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