Stress release via thermodynamic regulation towards efficient flexible perovskite solar cells†

Abstract

Flexible perovskite solar cells (f-PSCs) have garnered increasing research interest owing to their high power-to-weight ratio and ability to integrate into buildings. However, the mismatch of the thermal expansion coefficient between a perovskite film and substrate results in strain in the perovskite layer, which significantly impairs the photovoltaic and mechanical performance of f-PSCs. Herein, a thermodynamic regulation strategy was proposed to release the stress of perovskite film, realizing highly efficient f-PSCs with excellent flexibility. Camphor exhibited a strong affinity with Pb²⁺ or FA⁺ due to the strong electronegativity of the carbonyl functional group. During annealing, the sublimation of camphor exerted a force on the compressed lattice, driving the transformation of the distorted [PbI₆]⁴⁻ into a symmetry arrangement. Furthermore, the camphor-modified perovskite film exhibited lower defect state density, and the obtained f-PSCs achieved a power conversion efficiency of 24.48%, which exhibited outstanding mechanical and operational stability.