α-FA_1-xCs_xPbI₃ is a promising absorber material for efficient and stable perovskite solar cells (PSCs)^1,2. However, the most efficient α-FA_1-xCs_xPbI₃ PSCs require the inclusion of methylammonium chloride (MACl) additive^3,4, which generates volatile organic residues (i.e., MA) that limit device stability at elevated temperatures⁵. To date, the highest certified power-conversion efficiency (PCE) of α-FA_1-xCs_xPbI₃ PSCs without MACl was only ~24% (ref.^6,7), and has yet to exhibit any stability advantages. Here, we identify interfacial contact loss caused by the Cs⁺ accumulation for the conventional α-FA_1-xCs_xPbI₃ PSCs, which deteriorates the device performance and stability. Through in-situ GIWAXS analysis and DFT calculations, we demonstrate an intermediate phase-assisted crystallization pathway enabled by acetate surface coordination to fabricate high-quality α-FA_1-xCs_xPbI₃ film, without using MA-additive. We herein report a certified stabilized power output (SPO) efficiency of 25.94% and a reverse-scanning PCE of 26.64% for α-FA_1-xCs_xPbI₃ PSCs, exhibiting negligible contact losses and enhanced operational stability. The devices retain >95% of their initial PCEs after over 2,000 hours operating at maximum power point under 1 sun, 85 °C, and 60% relative humidity (ISOS-L-3).

α-FA _1-xCs_xPbI₃ 是一种很有前途的吸收材料，可用于高效稳定的钙钛矿太阳能电池 （PSC）^1,2。然而，最有效的 α-FA _1-xCs_xPbI₃ PSC 需要添加甲基氯化铵 （MACl）^{添加剂 3,4}，它会产生挥发性有机残留物（即 MA），从而限制装置在高温下的稳定性⁵。迄今为止，不含 MACl 的 α-FA _1-xCs_xPbI₃ PSC 的最高认证功率转换效率 （PCE） 仅为 ~24%（参考文献 ^6,7），尚未表现出任何稳定性优势。在这里，我们确定了传统 α-FA _1-xCs_xPbI₃ PSC 的 Cs⁺ 积累引起的界面接触损失，这恶化了器件的性能和稳定性。通过原位 GIWAXS 分析和 DFT 计算，我们展示了一种由乙酸盐表面配位实现的中间相辅助结晶途径，可在不使用 MA 添加剂的情况下制造高质量的 α-FA _1-xCs_xPbI₃ 薄膜。我们在此报告了 α-FA _1-xCs_xPbI₃ PSC 的认证稳定功率输出 （SPO） 效率为 25.94%，反向扫描 PCE 为 26.64%，表现出可忽略不计的接触损耗和增强的操作稳定性。这些设备在 1 个阳光、85°C 和 60% 相对湿度 （ISOS-L-3） 下以最大功率点运行 2,000 多个小时后，仍能保留 >95% 的初始 PCE。