Enhanced mechanical stability of perovskite film by modulating the toughness of grain boundary

Halide perovskite solar cells have attracted widespread attention in recent years due to their high photoelectric conversion efficiency. However, the cask effect from the brittleness of the polycrystalline perovskite films restricts their application in wearable devices. Herein, alkyl materials with different end groups are introduced into perovskite films to regulate the mechanical property of films. The experimental results demonstrate alkyl materials with special end groups such as –NH2 or –COOH can interact with perovskite and further improve the mechanical stability of films effectively. Especially, 5-ammonium valeric acid with bifunctional end groups of –NH2 and –COOH can strongly interact with adjacent perovskite grains and links them together to resist the formation of cracks during deformation. As a result, the average fracture energy of the perovskite film with 5-ammonium valeric acid is increased from 0.33 J/cm2 to 1.19 J/cm2 and the elastic modulus is reduced from 31.8 GPa to 2.57 GPa, leading to the high mechanical stability of perovskite solar cells. The work provides an innovative method to improve the toughness of perovskite films, thus opening up opportunities for the applications of perovskite solar cells in wearable electronics.