ZnO-Modified Anode for High-Performance SnO2-Based Planar Perovskite Solar Cells

Electron-transport layer (ETL) that promotes charge carrier separation and electron extraction is a key component of perovskite solar cells (PSCs). Here, we report a simple approach for improving carrier collection efficiency of PSCs by the ZnO-modified ITO in a low-temperature solution process. With the inset of a ZnO layer between the ITO substrate and the SnO2 ETL, the adverse energy band alignment can be eliminated and thus an Ohmic contact between the ITO and SnO2 ETL can be expected. Additionally, the scanning electron microscope images show that the SnO2 film deposited on the ZnO-modified ITO substrate has a lower surface roughness than those directly on the ITO, contributing to the formation of larger grain sizes and better crystalline properties of perovskite. On the basis of photoluminescence and impedance spectrum measurements, the addition of ZnO modification layer facilitates the efficient separation and transportation of photogenerated carriers from the perovskite absorber due to the improved contact resistance and electrical conductivity of ETL. Through such a simple approach, the PSC with the highest power conversion efficiency of 20.45% has been obtained. Our work highlights the importance of electrode/ETL contact and paves the way for further optimizing the performances of PSCs.