Hybrid-type quantum-dot cosensitized ZnO nanowire solar cell with enhanced visible-light harvesting

A polymer hybrid quantum-dot-sensitized solar cell was developed using CdSe/CdS/ZnO nanowires as a photoanode and regioregular P3HT as a conjugated polymer. The P3HT polymer was used as a hole transport material to replace the liquid electrolyte in quantum dot sensitized solar cells, CdSe/CdS acts as a cosensitizer, which enhances light harvesting in the visible range, and the ZnO nanowires provide a direct pathway for electron transport. Through an adequate cascade bandgap structure of the photoanode, the photoexcited electrons were effectively separated from the electron/hole pairs and transported under illumination. The remaining holes at the anode were transported by the conjugated polymer P3HT without any intermediate potential loss. The fabrication of the hybrid solar cell was optimized with various experimental conditions, including the length of the ZnO nanowires, quantum sensitizers, P3HT filling conditions, and electrolytes. The optimally obtained hybrid solar cells exhibited 1.5% power-conversion efficiency under AM 1.5G of 100 mW/cm(2) intensity. The fabricated hybrid cells exhibited highly durable cell performances, even after 1 month under atmospheric conditions, whereas the liquid junction quantum dot sensitized solar cells exhibited a significant degradation in their performances during the first 2 weeks immediately after fabrication. High open-circuit voltage and fill factor values of our hybrid quantum-dot-sensitized solar cell indicate that the applied hole transport layer efficiently dissociates electron/hole pairs at the interface and retards the interfacial charge recombination.