We show that adding ethylenediamine (EDA) to perovskite precursor solutions improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA_1–xCs_xPb(I_1–yBr_y)₃, which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol % EDA, we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a V_OC of 1.22 V and a champion maximum-power-point-tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA⁺ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties.

中文翻译：

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添加乙二胺可提高混合卤化物钙钛矿的性能并抑制相不稳定性

我们表明，在钙钛矿前体溶液中添加乙二胺 (EDA) 可提高高溴含量、无甲基铵、甲脒铯卤化铅钙钛矿 FA 1– x Cs x Pb(I 1– y Br _{y )}的_光伏器件_性能和材料_稳定性) ₃，目前对硅上钙钛矿串联太阳能电池很感兴趣。使用光谱学和高光谱显微镜，我们发现该添加剂提高了薄膜的均匀性并抑制了高溴钙钛矿配方中普遍存在的相不稳定性，从而生产出在环境条件下可保持 100 天以上稳定的薄膜。添加 1 mol% EDA 后，我们展示了 1.69 eV 间隙钙钛矿单结 pin 器件，其V _OC为 1.22 V，冠军最大功率点跟踪功率转换效率为 18.8%，与最佳报告相当不含甲基铵的钙钛矿。使用核磁共振 (NMR) 光谱和 X 射线衍射技术，我们表明 EDA 与 FA ^+反应在溶液中，快速定量地形成咪唑啉阳离子。正是在结晶过程中咪唑啉的存在推动了钙钛矿薄膜性能的改善。