Ferroelectric materials for photovoltaics have sparked great interest because of their switchable photoelectric responses and above-bandgap photovoltages that violate conventional photovoltaic theory. However, their relatively low photocurrent and power conversion efficiency limit their potential application in solar cells. To improve performance, conventional strategies focus mainly on narrowing the bandgap to better match the solar spectrum, leaving the fundamental connection between polar order and photovoltaic effect largely overlooked. We report large photovoltaic enhancement by A-site substitutions in a model ferroelectric photovoltaic material, BiFeO₃. As revealed by optical measurements and supported by theoretical calculations, the enhancement is accompanied by the chemically driven rotational instability of the polarization, which, in turn, affects the charge transfer at the band edges and drives a direct-to-indirect bandgap transition, highlighting the strong coupling between polarization, lattice, and orbital order parameters in ferroelectrics. Polar order engineering thus provides an additional degree of freedom to further boost photovoltaic efficiency in ferroelectrics and related materials.

中文翻译：

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通过极序工程增强铁电光伏效应。

用于光伏的铁电材料引起了人们极大的兴趣，因为它们的可切换光电响应和带隙以上的光电压违反了常规的光伏理论。然而，它们相对较低的光电流和功率转换效率限制了它们在太阳能电池中的潜在应用。为了提高性能，常规策略主要集中在缩小带隙以更好地匹配太阳光谱，而极性次序和光伏效应之间的基本联系却被大大忽略了。我们报告了在模型铁电光伏材料BiFeO _3中通过A- site替代进行的大型光伏增强。如光学测量所揭示并得到理论计算的支持，增强作用伴随着极化的化学驱动旋转不稳定性，这反过来又影响了带边缘的电荷转移并驱动了直接至间接的带隙跃迁，这突出了铁电体中极化，晶格和轨道顺序参数之间的强耦合。极序工程因此提供了额外的自由度，以进一步提高铁电体和相关材料中的光伏效率。