The fullerene C₆₀ is commonly applied as the electron transport layer in high-efficiency metal halide perovskite solar cells and has been found to limit their open circuit voltage. Through ultra-sensitive near-UV photoelectron spectroscopy in constant final state mode (CFSYS), with an unusually high probing depth of 5–10 nm, the perovskite/C₆₀ interface energetics and defect formation is investigated. It is demonstrated how to consistently determine the energy level alignment by CFSYS and avoid misinterpretations by accounting for the measurement-induced surface photovoltage in photoactive layer stacks. The energetic offset between the perovskite valence band maximum and the C₆₀ HOMO-edge is directly determined to be 0.55 eV. Furthermore, the voltage enhancement upon the incorporation of a LiF interlayer at the interface can be attributed to originate from a mild dipole effect and probably the presence of fixed charges, both reducing the hole concentration in the vicinity of the perovskite/C₆₀ interface. This yields a field effect passivation, which overcompensates the observed enhanced defect density in the first monolayers of C₆₀.

中文翻译：

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LiF中间层在钙钛矿太阳能电池中的场效应钝化

富勒烯 C ₆₀通常用作高效金属卤化物钙钛矿太阳能电池中的电子传输层，并且已被发现可限制其开路电压。通过恒定终态模式 (CFSYS) 下的超灵敏近紫外光电子能谱，具有 5-10 nm 的异常高探测深度，研究了钙钛矿/C ₆₀界面能量学和缺陷形成。演示了如何通过 CFSYS 一致地确定能级对齐，并通过考虑光活性层堆叠中测量引起的表面光电压来避免误解。钙钛矿价带最大值与 C _{60之间的能量偏移}HOMO-edge直接确定为0.55 eV。此外，在界面处加入 LiF 中间层后的电压增强可归因于温和的偶极子效应和可能存在固定电荷，两者都降低了钙钛矿/C ₆₀界面附近的空穴浓度。这产生了场效应钝化，其过度补偿了在C ₆₀的第一单层中观察到的增强的缺陷密度。