Super Strong Bonding at the Interface between ETL and Perovskite for Robust Flexible Optoelectronic Devices.

Organic-inorganic hybrid perovskites have demonstrated great potential for flexible optoelectronic devices due to their superior optoelectronic properties and structural flexibility. However, mechanical deformation-induced cracks at the buried interface and delamination from the substrate severely constrain the optoelectronic performance and device lifespan. Here, we design a two-site bonding strategy aiming to reinforce the mechanical stability of the SnO/perovskite interface and perovskite layer using a multifunctional organic salt, 4-(trifluoromethoxy)phenylhydrazine hydrochloride (TPH). This approach significantly enhances the bonding at the buried interface between the electron transport layer and perovskite layer, which is demonstrated by TPH-modified SnO/perovskite interface remaining intact after 10,000 bending cycles. Meanwhile, TPH mitigates void formation, enhances perovskite crystallinity at the buried interface, and inhibits ion migration inside the devices. Furthermore, incorporating TPH in perovskite bulk decreases the nucleation activation energy and accelerates nucleation, leading to high-quality perovskite film. Consequently, power conversion efficiencies (PCEs) of 21.64 % and 23.61 % are achieved for target flexible and rigid perovskite solar cells, respectively. The target flexible device retained 92.3 % of its initial PCE after 25,000 bending cycles. This approach provides a robust solution for enhancing the mechanical durability of flexible perovskite optoelectronic devices.