Unraveling Differences in the Effects of Ammonium/Amine‐Based Additives on the Performance and Stability of Inverted Perovskite Solar Cells

Abstract Additive engineering, with its excellent ability to passivate bulk or surface perovskite defects, has become a common strategy to improve the performance and stability of perovskite solar cells (PVSCs). Among the various additives reported so far, ammonium salts are considered an important branch. It is worth noting that although both ammonium‐based additives (R‐NH 3 + ) and amine‐based additives (R‐NH 2 ) are derivatives of ammonia (NH 3 ), the functions of the two can be easily confused due to their structural similarities. Moreover, there is no comprehensive comparative analysis of them in the literature. Here, the differences between phenethylammonium iodide (PEA + ) and phenethylamine (PEA) additives are revealed experimentally and theoretically. The results clearly show that PEA outperforms PEA + in terms of device performance and stability based on the following three factors: i) PEA's defect passivation capability is superior to that of PEA + ; ii) PEA has better hydrophobicity to hinder water ingress; and iii) PEA completely improves the stability of PVSCs by enhancing thermal stability and inhibiting iodide migration in perovskite more effectively than PEA + . As a result, the power conversion efficiency (PCE) of the inverted methylammonium triiodide (MAPbI 3 ) device using PEA increases by ≈15% to over 21%. More importantly, this device exhibits greater ability to prevent water invasion, thermal‐induce degradation, and inhibit iodide ion migration, resulting in better long‐term stability.