Fundamental Aspects of Photoinduced Charge Flow at a Quantum-Dot-Sensitized Single-Crystal TiO₂ Semiconductor Interface

The fundamental aspects of charge transfer from photoexcited CdSe quantum dots to a single crystal of TiO₂, a wide band gap metal oxide semiconductor, were investigated and compared with that of a dye-sensitized system in relation to the operation of quantum-dot-sensitized solar cells (QDSCs) and dye-sensitized solar cells (DSSCs). Due to the stark differences in both physical and electronic properties of quantum dots versus molecular dyes, it was hypothesized that the fundamental behavior of the two systems could differ greatly. The large size and surface area of the quantum dots relative to molecular dyes present the possibility for the positively charged hole to move a greater distance away from the QD/oxide interface during the electron injection process. This increased distance influences the Coulombic interaction between the trapped hole and injected electron, leading to differences and increased complexity of the recombination pathways when compared to the dye system.