Characterization of Perovskite Solar Cells

XRD diffraction pattern was recorded by Empyrean (D8 Advance, Bruker) with Cu K-alpha radiation (λ = 0.15406 nm) with a scan step size of 0.03°. Morphology was assessed by a scanning electron microscope (Jsm-6510; JEOL Ltd., Japan). The time-resolved photoluminescence (TR-PL) of perovskite films was characterized by the Edinburgh Instruments FLS 980 fluorescence spectrometer. The performance parameters were measured under AM 1.5 G (1000 W m⁻²) using 1000 W xenon as the light source (VS-0851A; Yamashita Denso Co., Ltd, Japan), while a Keithley-2460 source meter was used for data collection. The light intensity was calibrated using an AvaSolar simulator system (Fluotime 300, picoquant). The J–V curve was performed from 1.8 V to −0.1 V at step −0.02 V for each point. EQE spectrum response for sub-cells was recorded on an EQE system (QE-R, Enli Technology Co., Ltd.), and the wavelength range of 300–800 nm & 500–1200 nm for top and bottom cells respectively. Similarly, the excitation light intensity is calibrated by a Si photodiode. A square shape mask with an area of 1.21 cm² was used during the J–V measurement.