Realizing 23.9% Flexible Perovskite Solar Cells via Alleviating the Residual Strain Induced by Delayed Heat Transfer

Flexible perovskite solar cells (pero-SCs) have aroused widespread interest because of their unique advantages in lightweight and portable electronics applications. However, the delayed heat transfer caused by plastic substrates can severely affect the reaction activity and diffusivity of cations during perovskite growth, resulting in spatial composition inhomogeneity and residual strain in the perovskite film. Here, a cross-linker 4,5-(3-methyloxetane) dicarboxylate imidazole (MZ) is designed to regulate crystallization kinetics precisely for controlling composition distribution in perovskite films on plastic substrates. The MZ can coordinate with Pb2+ to form a mesoporous scaffold of lead iodide film and increase the activation energy for perovskite crystal formation, which can inhibit cation reaction in the top region and accelerate their downward diffusion. Consequently, the compositional inhomogeneity and residual strain can be effectively alleviated. Finally, the 0.062 and 1.004 cm2 flexible pero-SCs achieved record power conversion efficiencies of 23.94% (certified 23.57%) and 21.87% with enhanced operational and mechanical stability.