Speedy two-step thermal evaporation process for gold electrode in a Perovskite solar cell

We propose a speedy two-step deposit process to form an Au electrode on hole transport layer(HTL) without any damage using a general thermal evaporator in a perovskite solar cell(PSC). An Au electrode with a thickness of 70 nm was prepared with one-step and two-step processes using a general thermal evaporator with a 30 cm source-substrate distance and 6.0 × 10^-6 torr vacuum. The one-step process deposits the Au film with the desirable thickness through a source power of 60 and 100 W at a time. The two-step process deposits a 7 nm-thick buffer layer with source power of 60, 70, and 80 W, and then deposits the remaining film thickness at higher source power of 80, 90, and 100W. The photovoltaic properties and microstructure of these PSC devices with a glass/FTO/TiO₂/perovskite/ HTL/Au electrode were measured by a solar simulator and field emission scanning electron microscope. The one-step process showed a low depo-temperature of 88.5 °C with a long deposition time of 90 minutes at 60 W. It showed a high depo-temperature of 135.4 °C with a short deposition time of 8 minutes at 100 W. All the samples showed an ECE lower than 2.8% due to damage on the HTL. The two-step process offered an ECE higher than 6.25% without HTL damage through a deposition temperature lower than 88 °C and a short deposition time within 20 minutes in general. Therefore, the proposed two-step process is favorable to produce an Au electrode layer for the PSC device with a general thermal evaporator.