The last five years have witnessed remarkable progress in the field of lead halide perovskite materials and devices. Examining the existing body of literature reveals staggering inconsistencies in the reported results among different research groups with a particularly wide spread in the photovoltaic performance and stability of devices. In this work we demonstrate that fractional, quite possibly unintentional, deviations in the precursor solution stoichiometry can cause significant changes in the properties of the perovskite layer as well as in the performance and stability of perovskite photovoltaic devices. We show that while the absorbance and morphology of the layers remain largely unaffected, the surface composition and energetics, crystallinity, emission efficiency, energetic disorder and storage stability are all very sensitive to the precise stoichiometry of the precursor solution. Our results elucidate the origin of the irreproducibility and inconsistencies of reported results among different groups as well as the wide spread in device performance even within individual studies. Finally, we propose a simple experimental method to identify the exact stoichiometry of the perovskite layer that researchers can employ to confirm their experiments are performed consistently without unintentional variations in precursor stoichiometry.

中文翻译：

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前体化学计量的分数偏差决定了钙钛矿光伏器件的性能，性能和稳定性†

在过去的五年中，钙钛矿卤化铅材料和器件领域取得了显着进步。对现有文献进行审查后发现，不同研究小组之间报告的结果存在惊人的不一致，其中光伏性能和器件的稳定性尤为广泛。在这项工作中，我们证明了前体溶液化学计量的微小偏差（很可能是无意的）会导致钙钛矿层性能以及钙钛矿光伏器件的性能和稳定性发生重大变化。我们表明，尽管各层的吸收率和形态基本不受影响，但表面成分和能级，结晶度，发射效率，高能紊乱和贮存稳定性都对前体溶液的精确化学计量非常敏感。我们的结果阐明了不同组之间报告的结果的不可重复性和不一致之处，以及即使在个别研究中设备性能的广泛分布。最后，我们提出了一种简单的实验方法来确定钙钛矿层的精确化学计量，研究人员可以使用该方法来确认他们的实验是一致进行的，而不会造成前驱体化学计量的意外变化。