Facile Conversion Synthesis of Densely-Formed Branched ZnO-Nanowire Arrays for Quantum-Dot-Sensitized Solar Cells

• 3-D hierarchically branched ZnO nanowires by a facile synthesis with seed nucleation.
• Nanobranching enhances the efficiency by a factor of two compared with the bare QDSC.
• Attributed to the increased sensitizer by ∼80% and decreased transmittance by ∼17%.
• Optimized nanostructures correlate with the light-harvesting and carrier-collection efficiencies.

An effective way of synthesizing densely-formed branched ZnO-nanowire arrays was developed by a straightforward conversion reaction of ZnS into ZnO. Hierarchically structured ZnO nanowires are utilized for quantum-dot-sensitized solar cells (QDSCs), having resulted in the conversion-efficiency enhancement by a factor of two compared to the bare ZnO nanowires. This is attributed to the increased CdS-quantum-dot sensitizer by ∼80% and decreased diffused transmittance by ∼17%, induced by the densely-formed branched nanowires. The correlations between the branched nanostructures and photovoltaic performances are systematically investigated in terms of light absorption, charge-transfer resistance, and carrier lifetime. This facile and controllable branched nanowire synthesis is anticipated to be applicable to other semiconductor photoanodes for efficient light harvesting and charge collecting properties.