Low-temperature, high-speed reactive deposition of metal oxides for perovskite solar cells

Nickel oxide (NiO) and titanium dioxide (TiO2) charge-extraction layers are fabricated under a partial pressure of O-2 from nickel and titanium metals using a reactive electron-beam evaporation process. Using such materials, inverted architecture perovskite solar cells incorporating a NiO hole-transport layer achieve power conversion efficiencies up to 15.8%, whilst standard architecture devices using a TiO2 electron-transport layer achieve a power conversion efficiency up to 13.9%. Critically, we find that such metal oxides can be deposited at high speed (nm s(-1)) and at low substrate-temperature, and do not require a high-temperature anneal step after deposition, making reactive electron-beam evaporation compatible with roll-to-roll processing on sensitive flexible polymeric substrates.