Compositional engineering has led to dramatic improvements in hybrid perovskite-based solar cell stabilities and performance. Mixed cation perovskites have emerged as champion photovoltaic materials with power conversion efficiencies exceeding 22%. However, there has been relatively little work done to explore local cation-related compositional inhomogeneities in mixed cation perovskite films. Such studies are necessary because hybrid perovskite optical properties and, consequently, their photovoltaic performance strongly depend on composition. Here, we perform spatially resolved, subdiffraction infrared photothermal heterodyne imaging measurements to probe cation-specific compositional distributions within FA_xMA_1–xPbI₃ perovskite films. Our measurements reveal that these perovskites possess large compositional spatial heterogeneities with cation distributions varying on average ∼20% from expected ensemble stoichiometries. Correlated emission measurements show intrafilm emission energies differing by over 30 meV due to these compositional differences. These measurements thus reveal cation stoichiometric heterogeneities and their direct impact on local photovoltaic response-determining optical properties of mixed cation perovskites.

中文翻译：

---

混合阳离子钙钛矿的亚衍射红外成像：探测局部阳离子异质性

成分工程技术极大地改善了基于钙钛矿的混合太阳能电池的稳定性和性能。混合阳离子钙钛矿已成为光伏材料的冠军，其功率转换效率超过22％。然而，在混合阳离子钙钛矿薄膜中探索与局部阳离子有关的组成不均匀性的工作很少。这种研究是必要的，因为混合钙钛矿的光学性质以及因此的光伏性能在很大程度上取决于组成。在这里，我们执行空间分辨的亚衍射红外光热外差成像测量，以探测FA _x MA _{1– x} PbI ₃内的阳离子特定组成分布钙钛矿膜。我们的测量结果表明，这些钙钛矿具有较大的组成空间异质性，阳离子分布与预期的整体化学计量比平均相差约20％。相关的发射测量结果表明，由于这些组成差异，膜内发射能量相差30 meV以上。因此，这些测量结果揭示了阳离子化学计量的异质性及其对决定混合阳离子钙钛矿的光学性能的局部光伏响应的直接影响。