Core-shell CuInS₂/ZnS quantum dots assembled on short ZnO nanowires with enhanced photo-conversion efficiency

A novel quantum-dot-based solar cell assembly consisting of core-shell Zn-doped CuInS₂@ZnS (Zn-CIS@ZnS) quantum dots associated with short ZnO (5 μm in length) nanowires was developed and systematically investigated in terms of its nanostructure and optical properties, associated with corresponding solar cell parameters, i.e., V_OC, J_SC, fill factor (FF). In this investigation, the photo-conversion efficiency of the Zn-CIS-based solar cells without the presence of the ZnS shell can be readily tuned by controlling the Zn/Cu ratio. Furthermore, the efficiency was significantly improved upon the deposition of a thin ZnS shell on these Zn-CIS QDs, where a significant enhancement in short-circuit current density (J _SC) by 88% was observed because the ZnS coating is able to effectively eliminate excited electron recombination and enhance the charge transfer efficiency from Zn-CIS QDs to ZnO nanowires. Power-conversion efficiency as high as 0.71% can be attained, which is improved more than 2-3 times compared with that without ZnS coating. Such a unique nanoarchitecture through coupling with both core-shell QDs and short ZnO nanowires suggests a promising design for a quantum dot-based solar cell with considerably improved power-conversion efficiency.