In Situ Ferroelectric Built-in Field and Epitaxial Templating via Interfacial EATPbI ₄ Layer for Efficient Perovskite Solar Cells

Interfacial engineering is critical for efficient charge extraction in perovskite solar cells. However, conventional molecular passivation or lower-dimensional modulation at the buried interface suffers from stress mismatch and weak dipole interaction. Herein, we report an innovative approach involving the in situ construction of a two-dimensional ferroelectric interfacial layer to boost the built-in field and enhance charge extraction. Moreover, the interlayer also acts as a template for the epitaxial growth of 3D FAPbI 3 crystals, resulting in the formation of a highly oriented 3D perovskite film with reduced strain and defect density. The optimized rigid device achieves an impressive power conversion efficiency of 26.32% (certified at 25.60%) with a near-radiative-limit V OC of 1.20 V, and the flexible counterpart achieves remarkable efficiency of 25.01%. This strategy simultaneously solves the critical challenges of defect passivation, crystallographic control, and polarization-enhanced charge dynamics, establishing a versatile interfacial engineering paradigm for perovskite solar cells.