Intermediate Phase Free α-FAPbI Perovskite via Green Solvent Assisted Perovskite Single Crystal Redissolution Strategy.

Perovskite single-crystal redissolution (PSCR) strategy is highly desired for efficient formamidinium lead triiodide (FAPbI ) perovskite photovoltaics with enhanced phase purity, improved film quality, low trap-state density, and good stability. However, the phase transition and crystallization dynamics of FAPbI remain unclear in the PSCR process compared to the conventional fabrication from the mixing of precursor materials. In this work, a green-solvent-assisted (GSA) method is employed to synthesize centimeter-sized α-FAPbI single crystals, which serve as the high-purity precursor to fabricate perovskite films. The α-FAPbI PSCR strategy facilitates direct α-phase formation and inhibits the complex intermediate phases monitored by in situ grazing-incidence wide-angle X-ray scattering. Moreover, the α-phase stability is prolonged due to the relaxation of the residual lattice strain through the isotropic orientation phase growth. Consequently, the GSA-assisted PSCR strategy effectively promotes crystallization and suppresses non-radiative recombination in perovskite solar cells, which boosts the device efficiency from 22.08% to 23.92% with significantly enhanced open circuit voltage. These findings provide deeper insight into the PSCR process in terms of its efficacy in phase formation and lattice strain release. The green low-cost solvent may also offer a new and ideal solvent candidate for large-scale production of perovskite photovoltaics.