Thermally Stable Lead-free Tin Halide Perovskite Solar Cells Prepared from a Dimethyl Sulfoxide Free Perovskite Precursor Ink

The stability of lead-free tin halide perovskite solar cells (Sn–PSCs) at 85 °C is discussed from the viewpoint of the solvents used in each layer. The anhydrous poly(3,4-ethylenedioxythiophene) (PEDOT) complex hole transport layer (PEDOT-toluene) prepared from a toluene solution exhibited better thermal stability than PEDOT/PSS (PEDOT-water) prepared from an aqueous solution. Furthermore, we studied the effects of dimethyl sulfoxide (DMSO), which is used as a precursor ink for tin halide perovskites (Sn-PVKs), on the efficiency because DMSO promotes the oxidation of Sn2+ to Sn4+ in Sn-PVKs. To replace DMSO, we developed a DMSO free Sn-PVK precursor ink incorporating 2-methylaminopyridine. When the DMSO free ink was used during Sn-PSC formation, Sn4+ formation on the Sn-PVK film surface was particularly suppressed. The Sn–PSCs prepared using the DMSO free ink exhibited considerably improved stability at 85 °C. Our findings suggest that removing moisture present in the hole transport layer and using DMSO, an oxidizing solvent, are important for improving the thermal stability of Sn–PSCs.