P-type solar cells sensitized by ternary quantum dots

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Oral, Jinhyung Park, presentation 134
Publication date: 5th February 2015

Quantum dots (QDs) have a series of important properties such as high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to the quantum confinement, possibility of multiple exciton generation, which makes them a very attractive material for their applications in different technological areas, including photovoltaic devices.¹ QD solar cells are mainly focused on highly toxic cadmium and lead chalcogenides, which make the future commercial application doubtful based on health and environmental issues. In this respect,development of “eco-friendly” quantum dots without heavy elements is thus of high importance. Ternary and quaternary nanocrystals combine the classical advantages of QDs with their non-toxicity and possibility to fine tune their properties in a larger range due to the wider choice of composition.²< In a typical QD sensitized solar cell the nanocrystals are deposited onto the nanostructured electrode such as TiO₂ and upon the light absorption they inject electrons into the conduction band of the n-type material, while the hole is regenerated by the electrolyte. It is of high importance to develop and study the cells with the absorber injecting a hole into the valence band of a p-type material as it opens the way to tandem cells. So far the performances of such p-type cells lag far behind those of n-type ones mainly because of (i) strong recombination of typically used organic dye absorbers with p-type electrodes upon injection and (ii) lack of appropriate p-type materials which should combine good conductivity with high transparency. We act on both these limitations: (i) to use ternary QDs as sensitizers because they provide for the possibility of tuning the energy levels to minimize the recombination losses and maximize the hole injection; and (ii) to use new p-type nanostructured materials as electrodes with desired properties. We have used CuInS₂ and CuInS_xSe_2-x QDs as light absorbers and deposited them first on a mesoporous p-type NiO electrode. By fine-tuning their energy levels through varying their size, doping and surface ligands we have achieved an efficiency 1% (0.7% in average), which is comparable to the p-type DSSC record (1.3%)³and by far the best value reported for any p-type QD-sensitized cell. Preliminary results on the sensitization of p-type CuSCN nanowires recently designed by us with ternary quantum dots will also be presented.

1) Kamat, P. V. Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters. J. Phys. Chem. C, 2008, 112, 18737-18753. 2) Aldakov,D.; Lefrançois, A.; Reiss, P. Ternary and quaternary metal chalcogenide nanocrystals: synthesis, properties and applications. J. Mater. Chem., 2013, 1, 3756-3776. 3) Powar, S.; Daeneke, T.; Ma, M. T.; Fu, D.; Duffy, N. W.; Götz, G.; Weidelener, M.; Mishra, A.; Bäuerle, P.; Spiccia, L.; Bach, U. Highly Efficient p-Type Dye-Sensitized Solar Cells based on Tris(1,2-diaminoethane)Cobalt(II)/(III) Electrolytes. Angew. Chem. Int. Ed., 2013, 52, 602–605.

© FUNDACIO DE LA COMUNITAT VALENCIANA SCITO