Theoretical prediction and design for chalcogenide-quantum-dot/TiO₂ heterojunctions for solar cell applications

Quantum dot sensitized solar cells have attracted much attention due to their high efficiency of photoelectric conversion and low manufacturing cost. In this study, a series of heterojunction structures with cubic (MA)₄ chalcogenide quantum dots adsorbing on the (001) surface of TiO₂ were investigated, in order to explore new quantum dot sensitizers for solar cell applications. Our study revealed that sulfide and selenide quantum dots are more suitable for solar energy harvesting, compared to their oxide counterparts, due to their smaller ionization potentials and smaller HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gaps, but in general exhibit weaker adsorption on TiO₂. M₄A₃B and M₄A₂B₂ quantum dots were designed in combination with the advantage of higher adsorption stability and photoelectric conversion capability. Our theoretical predictions for the structurally precise chalcogenide systems suggest a possible direction for the design of quantum-dot sensitized solar cells.