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 twodimensional (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 N-2 atmosphere.