PbI2 interface reconstruction suppresses ion migration for stable planar perovskite solar cells

Abstract

Excess PbI₂ is widely recognized as a critical factor in enhancing the efficiency of perovskite solar cells, yet the random aggregated PbI₂ undergoes photodecomposition, and the migration of I⁻ remains a critical bottleneck for long-term device operation. Herein, we report a PbI₂ multi-interface reconstruction strategy enabled by the thermotropic liquid crystal molecule of 4-butoxybenzylidene-4-cyanoaniline (BBCA). During annealing, the dynamic phase transition of BBCA, along with its oriented arrangement and ordered self-assembled stacking, drives the formation of the (PbI₂)₂RbCl secondary phase and redistributes PbI₂ from the buried interface and grain boundaries to the upper surface. This process realizes synergistic PbI₂ reconstruction across multi-interfaces, effectively suppressing light- and heat-induced side reactions. Moreover, BBCA reduces defect density and non-radiative recombination losses, and optimizes the energy barrier, enhancing the PCE from 22.85% to 25.14%. Additionally, BBCA acts as a stabilizer by inhibiting both I⁻ oxidation and migration under operation, thereby enhancing device stability. This work introduces a novel strategy for controlling PbI₂ content and distribution across multi-interfaces while simultaneously suppressing ion migration, enabling highly efficient and stable perovskite solar cells.