Non‐Preheating Processed Quasi‐2D Perovskites for Efficient and Stable Solar Cells

Abstract Although the hot‐casting (HC) technique is prevalent in developing preferred crystal orientation of quasi‐2D perovskite films, the difficulty of accurately controlling the thermal homogeneity of substrate is unfavorable for the reproducibility of device fabrication. Herein, a facile and effective non‐preheating (NP) film‐casting method is proposed to realize highly oriented quasi‐2D perovskite films by replacing the butylammonium (BA⁺) spacer partially with methylammonium (MA⁺) cation as (BA)_2−x(MA)_3+xPb₄I₁₃ (x = 0, 0.2, 0.4, and 0.6). At the optimal x‐value of 0.4, the resultant quasi‐2D perovskite film possesses highly orientated crystals, associated with a dense morphology and uniform grain‐size distribution. Consequently, the (BA)_1.6(MA)_3.4Pb₄I₁₃‐based solar cells yield champion efficiencies of 15.44% with NP processing and 16.29% with HC processing, respectively. As expected, the HC‐processed device shows a poor performance reproducibility compared with that of the NP film‐casting method. Moreover, the unsealed device (x = 0.4) displays a better moisture stability with respect to the x = 0 stored in a 65% ± 5% relative humility chamber.