“…Among the metal oxides, ZnO is widely used ETL in OSCs due to its high transmittance, mobility and conductivity . There are different kind of routes for deposition or preparation of ZnO ETL such as spray pyrolysis, sputtering, nanoparticle synthesis, sol–gel method, and so on. , Sol–gel is the most preferred and used technique with the advantages of easy solution processing at low temperature, low cost, uniform thickness throughout the layer, and compatibility for large-area deposition. − Different ETLs and performance in the OSCs are illustrate in the Table .…”