Quantum dot sensitized solar cells

Metal sulfide (CdS or PbS) quantum dots were synthesized in nanoporous TiO₂ films for applications in solar energy conversion devices. Several electrolytes were investigated for the functioning redox activity in sandwich type regenerative solar cells, based on the quantum dots sensitized TiO₂ film. A high IPCE was attained by optimizing the polysulfide electrolyte composition. The CdS QD shows a higher IPCE, compared to PbS, related to an increased light harvesting efficiency when the number and size of the QDs intensified. In contrast, QD size dependence on the IPCE was observed for the PbS, likely resulting from the conduction band edge potential shift (associated with quantum size effect) relative to the TiO₂ conduction band edge, or the kinetic competition between the hot electron injection and the electron relaxation in the PbS conduction band. We also propose that an I₃ ^-/I^- redox electrolyte, with NaSCN addition, can be employed to enhance the solar cell performance. SCN^- ions may attach to the QD surface forming a shell type structure to prevent the photocorrosion reaction, and act as an intermediate electronic state to induce the sequential step electron transfer reactions for the QD re-reduction.