Regulating lattice evolution via an ordered two-dimensional intermediate phase for resilient perovskite solar cells

The dynamic expansion and contraction of metal halide hybrid perovskite lattices during day-night cycling generate severe mechanical strain, accelerating trap accumulation and device degradation. Here, we show a strain-regulation strategy that employs a highly oriented two-dimensional (2D) perovskite, 1-(p-fluorophenyl)biguanide lead iodide, as an ordered intermediate phase to template the vertically oriented growth of the (100) crystal plane of the bulk perovskite layer. During the subsequent thermal annealing process, this 2D intermediate decomposes to release PbI₂, which directly participates in the crystallization of the three-dimensional (3D) bulk layer. This spatial enhancement of lattice orientation suppresses photo- and thermal-induced lattice expansion and minimizes lattice distortion from 0.22% to 0.09%, thereby mitigating structural deterioration during dynamic operational cycles. Consequently, planar n-i-p Cs_0.05MA_0.05FA_0.9PbI₃ perovskite solar cells achieve outstanding power conversion efficiencies of 26.32 % for small-area devices (0.06 cm²) and 22.25 % for large-area modules (16.8 cm²) under one sun illumination. Furthermore, unencapsulated devices retain over 92% of their initial efficiency after 1,800 hours of continuous maximum power point tracking in an N₂ atmosphere. Notably, the devices exhibit robust diurnal stability, preserving over 89% of their initial efficiency after 40 rigorous light-dark cycles.