2D perovskite or organic material matter? Targeted growth for efficient perovskite solar cells with efficiency exceeding 24%

Defects at the surface and grain boundaries at the interface between perovskite and electron transport layer (ETL) induce severe non-radiative recombination, detrimental to device's performance and stability. Organic materials are often used for surface passivation, but most works ascribed the great passivation ability to the formed two-dimensional (2D) perovskite. Here, we demonstrated that the organic halide salt hexaneammonium iodide (HAI) targets growth at grain boundaries and plays a critical role in suppressing the charge recombination instead of forming quasi-2D or 2D perovskite to passivate the surface defects. Moreover, the HAI invested the perovskite films with superhydrophobicity, enhancing the moisture resistance and preventing the diffusion of Li+ into perovskite films. As a result, boosting the efficiency of PSCs from 22.38% to 24.07% (certified efficiency of 23.59%) with a voltage deficit of 0.35 V. The surface treatment also enhances the operational stability of perovskite solar cells (PSCs), unencapsulated devices maintain 81.4% of their initial efficiency for 200 h under continuous light irradiation in the N2 atmosphere.