Foldable Inverted Perovskite Solar Cells Enabled by Region-Dependent Microscopic and Macroscopic Strain Relaxation

Abstract

While foldable solar cells can advance the applications from emerging electronics like self-powered wearable optoelectronic devices, the poor mechanical durability of perovskite films due to the severe intrinsic strain, and the brittle nature of the flexible ITO electrode hinder foldable perovskite solar cells (F-PSCs) realization. Here, the strategy of region-dependent microscopic and macroscopic strain suppression is demonstrated to achieve efficient F-PSCs on silver nanowires (AgNWs) electrodes. Fundamentally, by introducing the region-dependent modification approach of functionalized polymer incorporation, the significant release of microscopic strain in perovskite film is demonstrated by effectively suppressing defects at places with crystallization orientation variation of perovskite surface/grain boundaries. Equally important, the gradient macroscopic strain is simultaneously eliminated by inhibiting the FA⁺ (formamidinum) gradient distribution in perovskite film's depth direction. The two-strain relaxations greatly enhance the mechanical durability of perovskite film, while also improving phase stability and suppressing ion migration. Finally, efficient F-PSCs (23% PCE, the highest value among reported F-PSCs) is realized with remarkable foldability, with efficiency maintaining 94% of its initial value even after 2000 times multidirectional folding at 0.75 mm curvature radius, which far exceeds the mechanical durability of typical ITO-based flexible PSCs. This work aids in comprehending strain modulation role for F-PSCs realization.