Efficient, stable solar cells by using inherent bandgap of α-phase formamidinium lead iodide

Maintaining the bandgap The bandgap of the black α-phase of formamidinium-based lead triiodide (FAPbI 3 ) is near optimal for creating high-efficiency perovskite solar cells. However, this phase is unstable, and the additives normally used to stabilize this phase at ambient temperature—such as methylammonium, caesium, and bromine—widen its bandgap. Min et al. show that doping of the α-FAPbI 3 phase with methylenediammonium dichloride enabled power conversion efficiencies of 23.7%, which were maintained after 600 hours of operation. Unencapsulated devices had high thermal stability and retained >90% efficiency even after annealing for 20 hours at 150°C in air. Science , this issue p. 749