Nanowire-based quantum-dot-sensitized solar cells

We report a quantum-dot-sensitized solar cell which combines CdSe quantum dots adsorbed on ZnO nanowires to convert light into electrical current flow. Specifically, an array of ZnO nanowires were grown vertically on a transparent conducting glass substrate in aqueous solutions of methenamine and zinc nitrate. CdSe quantum dots were synthesized separately and capped with mercaptopropionic acid. Following, the quantum dots were attached to the surface of the nanowires to form a photosensitized anode where the ZnO nanowire surfaces were decorated with a monolayer of CdSe quantum dots. A platinized transparent conducting oxide photocathode and the nanowire photoanode were positioned face-to-face and the space between the anode and the cathode was filled with an electrolyte. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dot-nanowire interface in to the ZnO nanowire. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the transparent conducting oxide anode. These solar cells exhibited short-circuit currents ranging from 1-2 mA/cm2 and open-circuit voltages of ∼0.6 V when illuminated with 100 mW/cm2 simulated AM1.5 spectrum. The internal quantum efficiency (IQE) of this QDSSC in the spectral range covering the first excitonic transition (∼500-600 nm) was 50-60%.