Nanowire-based quantum-dot-sensitized solar cells

A new kind of quantum-dot-sensitized solar cell that combines CdSe quantum dots adsorbed on ZnO nanowires to convert light into electrical current flow was described. An array of ZnO nanowires was grown vertically on a transparent and conducting glass substrate in aqueous solutions of methenamine and zinc nitrate at ∼ 95°C. Nanometer-size CdSe quantum dots were synthesized separately and capped with mercaptopropionic acid. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dot-nanowire interface into the ZnO nanowires. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the transparent conducting oxide anode. After the electron was injected into the ZnO, the positively-charged CdSe quantum dot was reduced through an electrochemical reaction with I- in the electrolyte to form I3- which in turn was reduced at the photocathode by an electron that has traveled across the load to complete the circuit. These solar cells exhibited short-circuit currents ranging from 1-2 mA/sq cm and open-circuit voltages of ∼ 0.6 v when illuminated with 100 mw/sq cm simulated AM1.5 spectrum. The overall conversion efficiency is limited by the availability of ZnO nanowire surface area for quantum dot adsorption. This is an abstract of a paper presented at the AIChE Annual Meeting (Salt Lake, UT 11/4-9/2007).