The importance of the TiO2/quantum dots interface in the recombination processes of quantum dot sensitized solar cells

Quantum dot sensitized solar cells (QDSSCs) present a promising technology for next generation photovoltaic cells, having exhibited a considerable leap in performance over the last few years. However, recombination processes occurring in parallel at the TiO2-QDs-electrolyte triple junction constitute one of the major limitations for further improvement of QDSSCs. Reaching higher conversion efficiencies necessitates gaining a better understanding of the mechanisms of charge recombination in these kinds of cells; this will essentially lead to the development of new solutions for inhibiting the described losses. In this study we have systematically examined the contribution of each interface formed at the triple junction to the recombination of the solar cell. We show that the recombination of electrons at the TiO2/QDs interface is as important as the recombination from TiO2 and QDs to the electrolyte. By applying conformal MgO coating both above and below the QD surface, recombination rates were significantly reduced, and an improvement of more than 20% in cell efficiency was recorded.