Improving Low-Bandgap Tin-Lead Perovskite Solar Cells via Contact Engineering and Gas Quench Processing

Low-bandgap Sn/Pb ABX₃ perovskites have reached photovoltaic power conversion efficiencies >20%, but they usually have poor stability due to the common use of acidic poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole transport layers and A-site cation compositions containing methylammonium (MA). Here, we develop a process to enable high-quality MA-free Sn/Pb perovskite films grown using a gas quenching process instead of the conventional antisolvents, which provides improved control of the film growth and eliminates wrinkling. Using this method in a device structure with poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) instead of PEDOT:PSS as the hole transport layer, devices can reach efficiencies up to 20%_mppt at 0.06 cm² and up to 17.5%_mppt at 1 cm² active area. With these improvements, the devices are characterized for thermal stability and show 80% of the initial power output remaining after 4000 h at 85 °C.