Buried Ultrathin Perovskite Layer Seeding Homogeneous Crystallization Toward Efficient Flexible Perovskite Solar Cells

ABSTRACT Flexible perovskite solar cells (f‐PSCs) are highly promising for lightweight, bendable, and integrable photovoltaic applications. However, fabricating high‐quality perovskite films on low‐temperature‐resistant plastic substrates remains a great challenge. This issue is particularly prominent in p‐i‐n type PSCs, where the self‐assembled monolayer (SAM) based buried interface suffers from inferior wettability and tends to induce undesirable phase transformation of perovskite. Herein, we propose an interfacial seeding strategy that introduces an ultrathin perovskite layer into the SAM layer prior to the deposition of perovskite films. This buried‐interface modification facilitates the homogeneous distribution of SAMs on the bottom electrode and enhances the affinity of the SAM surface toward the polar perovskite precursor, thereby improving perovskite coverage on the hydrophobic substrates. Moreover, the buried ultrathin perovskite serves as a well‐defined nucleation template that triggers the homogeneous crystallization of the upper perovskite layer. This significantly enhances the crystal quality and interfacial integrity, while suppressing defect states and reducing the Young's modulus of the perovskite films. As a result, a champion efficiency of 25.18% was achieved for f‐PSCs, accompanied by significantly improved resistance against long‐term storage, thermal aging, light exposure, and repeated bending.