Colloidal quantum dot solar cells (CQDSCs) based on one-dimensional metal oxide nanowires (NWs) as the electron transport layer (ETL) have attracted much attention due to their larger ETL/colloidal quantum dots (CQDs) contact area and longer electron transport length than other structure CQDSCs, such as planar CQDSCs. However, it is known that defect states in NWs would increase the recombination rate because of the high surface area of NWs. Here, the defect species on the ZnO NWs' surface which resulted in the surface recombination and SnO 2 passivation effects were investigated. Comparing with the solar cells using pristine ZnO NWs, the CQDSCs based on SnO 2 passivated ZnO NW electrodes exhibited a beneficial band alignment to charge separation, and the interfacial recombination at the ZnO/CQD interface was reduced, eventually resulting in a 40% improvement of power conversion efficiency (PCE). Overall, these findings indicate that surface passivation and the reduction of deep level defects in ETLs could contribute to improving the PCE of CQDSCs.

One-dimension ZnO nanowires (NWs) are widely used in many optoelectronic devices owing to their high optical transparency and excellent electron-transporting property. Unfortunately, there are various shallow-level and deep-level states in ZnO NWs, which usually act as the charge recombination centers of the devices. Surface passivation is an effective way to reduce deep-level states in ZnO NWs. However, how the surface passivation affects the charge dynamic process in ZnO NWs is still unclear. Herein, we carried out an in-depth study of the charge dynamics in surface-passivated ZnO NWs by using time-resolved photoluminescence and transient absorption spectroscopy techniques. The results show that the percentage of nonradiative recombination in ZnO NWs is efficiently reduced, and the lifetime of photoexcited carrier is increased after surface passivation. The introduction of a thin passivation layer like SnO 2 can effectively reduce the rate of interfacial charge recombination without any adverse effect on the electron injection process.