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

TLDR

Mixed cation and anion perovskite compositions are used to stabilize the black α‑phase of FA‑based lead triiodide, but additives such as MA, Cs, and Br widen its bandgap and lower thermal stability. Doping α‑FAPbI3 with methylenediammonium dichloride yields devices with certified Jsc of 26.1–26.7 mA cm⁻², a PCE of 23.7 %, and over 90 % of initial efficiency after 600 h of full‑sun MPPT operation, while unencapsulated cells retain >90 % of their PCE after 20 h at 150 °C and show better thermal and humidity stability than MAPbBr3‑stabilized controls.

Abstract

In general, mixed cations and anions containing formamidinium (FA), methylammonium (MA), caesium, iodine, and bromine ions are used to stabilize the black α-phase of the FA-based lead triiodide (FAPbI3) in perovskite solar cells. However, additives such as MA, caesium, and bromine widen its bandgap and reduce the thermal stability. We stabilized the α-FAPbI3 phase by doping with methylenediammonium dichloride (MDACl2) and achieved a certified short-circuit current density of between 26.1 and 26.7 milliamperes per square centimeter. With certified power conversion efficiencies (PCEs) of 23.7%, more than 90% of the initial efficiency was maintained after 600 hours of operation with maximum power point tracking under full sunlight illumination in ambient conditions including ultraviolet light. Unencapsulated devices retained more than 90% of their initial PCE even after annealing for 20 hours at 150°C in air and exhibited superior thermal and humidity stability over a control device in which FAPbI3 was stabilized by MAPbBr3.