Surface engineering of ZnO electron transporting layer via Al doping for high efficiency planar perovskite solar cells

Highlights: • Sputtered made, Al doped ZnO film can be applied as an electron transporting materials for high-efficiecny perovskite solar cell. • The atmosphere of the sputtering chamber can be used to control the properties of the resulting Al doped ZnO film. • The conductivity, acid resistance and band structure of the Al doped ZnO are key parameters effect the photovoltaic performance of the resulting cells. ZnO was known as a good electron transporting material for the planar perovskite solar cells (PSCs). The stability of perovskite cell based on ZnO electron transporting layer (ETL) however is not good, due to the basicity nature of ZnO, which will react with the proton on CH₃NH₃⁺ of perovskite. Doping was used successfully to modify the physicochemical properties of ZnO to improve the performance. High quality, fully covered Al doped ZnO (AZO) thin (~20 nm) film on ITO substrate was successfully prepared by a sputtering method. Compared to the cell based on ZnO, perovskite cell using AZO as ETL has better stability, comparable Jsc, higher Voc and FF. The best AZO based perovskite cell achieves the highest power conversion efficiency of 17.6% with Voc of 1.07 V which the highest Voc for the perovskite solar cell based on ZnO ETL. The improvement in the photovoltaic performance was due to AZO has higher conductivity, more resistance to the acid and better band matching with MAPbI₃ compared to ZnO. The highly conducting and transparent AZO film was also used to replace ITO/ZnO as an anode as well as the ETL in the planer perovskite cell to achieve the PCE of 6.3%.