You Lu, Zheng Fan, Fang Liang, Zhou Yang, Tan Liang Z, Zhang Zeyu, Ma Guohong, Schmidt Daniel, Rusydi Andrivo, Wang Le, Chang Lei, Rappe Andrew M, Wang Junling
School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
Sci Adv. 2018 Jul 6;4(7):eaat3438. doi: 10.1126/sciadv.aat3438. eCollection 2018 Jul.
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 -site substitutions in a model ferroelectric photovoltaic material, BiFeO. 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.
用于光伏的铁电材料因其可切换的光电响应和违反传统光伏理论的带隙以上光电压而引发了极大的兴趣。然而，它们相对较低的光电流和功率转换效率限制了其在太阳能电池中的潜在应用。为了提高性能，传统策略主要集中在缩小带隙以更好地匹配太阳光谱，而极性有序与光伏效应之间的基本联系在很大程度上被忽视了。我们报道了在一种典型的铁电光伏材料BiFeO₃中通过A位替代实现的大幅光伏增强。如光学测量所揭示并得到理论计算支持的那样，这种增强伴随着由化学驱动的极化旋转不稳定性，这反过来又影响了带边处的电荷转移并驱动了直接到间接的带隙转变，突出了铁电体中极化、晶格和轨道有序参数之间的强耦合。因此，极性有序工程为进一步提高铁电体及相关材料的光伏效率提供了额外的自由度。
