A crystal capping layer for formation of black-phase FAPbI3 perovskite in humid air

Editor’s summaryGrowth of the photoactive black phase of formamidinium lead iodide (α-FAPbI3) usually requires dimethyl sulfoxide solvent, but the hygroscopic nature of this chemical also promotes water-induced degradation to the photoinactive phase. Zou et al. showed that a larger chlorinated organic molecule can form a hydrophobic capping layer that enables perovskite crystallization under humid conditions by protecting growing crystallites from water. Solar cells were fabricated across a relative humidity range of 20 to 60% and reached power conversion efficiencies of 23.4% at 80% relative humidity. An unencapsulated device retained 96% of its initial performance in humid air after 500 hours of illumination at maximum power point operation. —Phil Szuromi