Phenethylammonium (PEA⁺) and butylammonium (BA⁺) are widely used in three-dimensional (3D) perovskites to form two-dimensional perovskites at film surfaces and grain boundaries (GBs) for defect passivation and performance enhancement. Here we show that these cations are unstable with 3D formamidinium (FA⁺)-containing perovskites under high-temperature light soaking. PEA⁺ and BA⁺ are found to deprotonate to amines, which then react with FA⁺ to produce (phenethylamino)methaniminium (PEAMA⁺) and (butylamino)methaniminium (BAMA⁺), respectively, severely limiting device high-temperature photostability. Removing these cations greatly improves the photostability but compromises device efficiency by leaving non-fully passivated surfaces and GBs. Ammonium cations with a high acid dissociation constant (pK_a), including PEAMA⁺ (pK_a = 12.0) and BAMA⁺ (pK_a = 12.0), can replace PEA⁺ or BA⁺ for passivation and are stable with FA-based perovskites due to their resistance to further deprotonation. P–i–n structure solar cells with PEAMA⁺ additive maintained over 90% of their initial efficiency after light soaking at open circuit and 90 °C for 1,500 hours.

苯乙基铵 (PEA ⁺ ) 和丁基铵 (BA ⁺ ) 广泛用于三维 (3D) 钙钛矿，在薄膜表面和晶界 (GB) 形成二维钙钛矿，用于缺陷钝化和性能增强。在这里，我们证明这些阳离子在高温光浸泡下与含 3D 甲脒 (FA ^{+ ) 的钙钛矿不稳定。}发现PEA ⁺和 BA ⁺去质子化为胺，然后胺与 FA ⁺反应生成(苯乙基氨基)甲胺 (PEAMA ⁺ ) 和 (丁氨基)甲胺 (BAMA ⁺）分别严重限制了器件的高温光稳定性。去除这些阳离子大大提高了光稳定性，但会留下未完全钝化的表面和GB，从而损害器件效率。具有高酸解离常数 (p K _a ) 的铵阳离子，包括 PEAMA ⁺ (p K _a  = 12.0) 和 BAMA ⁺ (p K _a  = 12.0)，可以代替 PEA ⁺或 BA ⁺进行钝化，并且与 FA- 保持稳定基于钙钛矿，因为它们能抵抗进一步的去质子化。^{具有 PE​​AMA +}的 P–i–n 结构太阳能电池在开路和 90 °C 下光浸泡 1,500 小时后，添加剂仍保持其初始效率的 90% 以上。