CdSe/ZnS Core/Shell Quantum Dot Sensitization of Low Index TiO2 Single Crystal Surfaces

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Abstract
Quantum dots (QDs) are actively explored as alternative sensitizers to inorganic complexes in sensitized solar cells (SSC) due to their interesting physical, optical, and electronic properties. It is thought that the inorganic nature of QDs should provide enhanced stability over the entirely organic or inorganic complex dyes, yet the long-term stability of laboratory QD-SSC devices has not been investigated in detail. A general approach to synthesize high stability QDs involves coating the core material with a wide band gap inorganic shell material (type-I CS QD). However, the electronic structure of the resulting core/shell (CS) structure has potential barriers for both electron and hole transfer, suggesting inefficient charge carrier separation for type-I CS QDs. Herein we demonstrate that type-I CdSe/ZnS CS QDs can effectively sensitize single crystal TiO2 electrodes and continue to operate in a regenerative mode in an aerated iodide electrolyte for more than 20 h. Core CdSe QDs degrade rapidly in the same electrolyte presumably due to CdI2 formation. The possibility of exploring new core/shell nanomaterials in a variety of electrolyte/mediator combinations may result in more efficient and stable QD-SSCs.