The role of the metal precursors and the surface passivation for the development of high performance Quantum Dot Sensitized Solar Cells
Juan Bisquert a, Rafael S. Sánchez a, Victoria González-Pedro a, Iván Mora-Seró a, Marina E. Rincón b, Mauricio Solís b, Pablo P. Boix c
a Universidad Nacional Autónoma de México, Centro de Investigación en Energía, Apartado Postal 34, Temixco, Mor., México 62580
b Technological University, School of Materials Science and Engineering, Singapore 639798, Singapore, Singapore
Oral, Rafael S. Sánchez, presentation 034
Publication date: 1st April 2013

The properties of Quantum Dot Sensitized Solar Cells (QDSCs) have been systematically characterized for CdS and CdS/ZnS and it is well-known that surface passivation plays an important role on the performance of the QD-based optoelectronic devices.1,2 However, we have observed that not only additional passivation treatments, but also the precursors utilized for the growing of the light absorber semiconductors may induce a significant effect on the overall efficiencies of the QDSC. Therefore, we show in this work that metal acetate (MOAc) precursors provide higher performance devices compared to those prepared from metal nitrate (MNO3) derivatives. Furthermore, we found out that the passivation effect strongly depends on the nature of the passivation agents; while species bearing a carboxylic acid group promote a decrease of the solar cell performance, compounds with thiol or amine groups promote a clear enhancement of the device efficiencies. The origin of this different behaviour may arise from the effect of the passivation on the: i) TiO2 conduction band; ii) charge recombination rate and/or iii) charge recombination nature, which is reflected in the variation of the β parameter.3 Especially interesting is the finding that β can be increased, and consequently the Fill Factor values, FF, are increased after the passivation. Applying this strategy, record cells of 4.65% efficiency for PbS based QDSCs have been prepared.

Figure 1: a) bare TiO2, CdS and PbS/CdS based electrodes deposited by SILAR method. b) J/V curves of a reference cell based on PbS/CdS light absorber and the record efficiency PbS/CdS cell passivated with EDT (η=4.65%).
1) Lee, Y. L.; Lo, Y. S. Adv. Funct. Mater. 2009, 19, 604. 2) Talapin, D. V.; Mekis, I.; Götzinger, S.; Kornowski, A.; Benson, O.; Weller, H. J. Phys. Chem. B 2004, 108, 18826. 3) Fabregat-Santiago, F.; Garcia-Belmonte, G.; Mora-Seró, I.; Bisquert, J. Phys. Chem. Chem. Phys. 2011,13, 9083.
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