Large Orientation Angle Buried Substrate Enables Efficient Flexible Perovskite Solar Cells and Modules

Abstract Flexible perovskite solar cells (f‐PSCs) have emerged as potential candidates for specific mechanical applications owing to their high foldability, efficiency, and portability. However, the power conversion efficiency (PCE) of f‐PSC remains limited by the inferior contact between perovskite and flexible buried substrate. Here, an asymmetric π‐extended self‐assembled monolayer (SAM) (4‐(9H‐dibenzo[a,c]carbazol‐9‐yl)butyl)phosphonic acid (A‐4PADCB) is reported as a buried substrate for efficient inverted f‐PSCs. Employing this design strategy, A‐4PADCB exhibits a significant orientation angle away from the surface normal, homogenizing the distribution of contact potentials. This enhancement improves the SAM/perovskite interface quality, controlling the growth of favorable perovskite films with low defect density and slight tensile stress. Integration of A‐4PADCB into small‐area f‐PSCs and large‐area flexible perovskite solar modules with an aperture area of 20.84 cm 2 achieves impressive PCEs of up to 25.05% and 20.64% (certified 19.51%), respectively. Moreover, these optimized A‐4PADCB‐based f‐PSCs possess enhanced light, thermal, and mechanical stability. This research paves a promising avenue toward the design of SAM‐buried substrates with a large orientation angle, regulating perovskite growth, and promoting the commercialization of large‐area flexible perovskite photovoltaics.