Fig. 4. PSC Operational Performance.

a Time-resolved photoluminescence (PL) transients of FAPbI₃ materials made using different fabrication methods. PL was detected at 810 nm following pulsed-laser excitations (398 nm at 2.5 MHz repetition rate) at an excitation fluence of 81 nJ cm^-2. PL lifetimes, τ_PL, determined by stretched exponential fits are shown on the figure labelling. Solid lines are stretched-exponential fits to the measured data. b Cross-sectional scanning electron microscopy image of PSC fabricated utilising 2D precursor phase-engineered α-FAPbI₃. J-V characteristics and corresponding maximum power point tracked efficiency (η_mpp) and current density (J_mpp) measured at maximum power point for champion devices fabricated from 2D precursor phase-engineered α-FAPbI₃ with illuminated area 0.25 cm² (c, e) and 1.00 cm² (d, f). Light J-V and η_mpp measurements were performed under simulated AM1.5 100.7 mWcm^-2 irradiance, accounting for the spectral mismatch factor. J_sc = short-circuit current density, V_oc = open-circuit voltage, FF = fill factor, V_mpp = maximum power point voltage.