Dye versus Quantum Dots in Sensitized Solar Cells: Participation of Quantum Dot Absorber in the Recombination Process

Inorganic quantum dots (QDs) show great potential as absorbers in sensitized solar cell, but there are open questions about the role of quantum dots, where primary electron and hole generation occurs, in the recombination process in this kind of solar cells. In opposition to the conventional dye-sensitized solar cell, here we show that inorganic QDs play a direct role in the recombination process. This fact has been determined by a fingerprint of QDs in the capacitance of the device, where the QDs surface states affect the density of states (DOS) distribution. It indicates that now surface states of QD contribute to the common DOS distribution of TiO₂/QDs/ZnS, which behaves as a single entity, being impossible to distinguish between TiO₂ and QDs. This result highlights the necessity of treating (and optimizing) QD-sensitized solar cells from another perspective than dye-sensitized solar cells, considering the fundamental differences in their behavior