Synergistic Zinc(II) and Formate Doping of Perovskites: Thermal Phase Stabilization of α-FAPbI₃ and Enhanced Photoluminescence Lifetime of FA_0.8MA_0.2PbI₃ up to 3.7 µs

Adding zinc (II) cations and formate anions improves the thermal phase stability of α-FAPbI₃ materials, and the spin-coated thin films of such doped FAPbI₃ (produced using MACl) show an increased emission lifetime of up to 3.7 μs on quartz (for FA_0.8MA_0.2PbI₃). This work investigates the effects of zinc and formate on the phase stability and time-resolved photoluminescence of FAPbI₃ perovskites for solar cell applications. Perovskite samples with varying concentrations of zinc and formate were made by incorporating different amounts of zinc formate and zinc iodide and were characterized with XRD. Doping levels of 1.7% Zn(II) and 1.0% formate (relative to Pb) seem optimal. The thermal phase stability of the doped perovskite powders (FAPbI₃) and thin films (FA_0.8MA_0.2PbI₃) was assessed. XRD of the thin films after 6 months shows only the alpha-phase. The time-resolved photoluminescence spectroscopy of the doped spin-coated perovskite samples (FA_0.8MA_0.2PbI₃ produced using MACl) is reported. The results show that synergy between an anionic and a cationic dopant can take place, making the perovskite thermally more phase-stable (not converting to the yellow delta-phase) with a longer charge carrier lifetime. In order to produce good thin films by spin coating, the use of MACl was essential.