Shift current is the dominant dc-current response in the bulk photovoltaic effect (BPVE), which is the conversion of solar energy into electricity in the materials with broken inversion symmetry. While the guiding principle of BPVE is a lack of inversion symmetry in a material which also results in ferroelectricity, it is therefore, expected that a significantly large shift current is achieved in ferroelectric materials. In this work, we calculate shift current using first principles in two-dimensional $\alpha \text{−}\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$ which has both in-plane and out-of-plane polarization at room temperature. To understand the implications of in-plane and out-of-plane polarization on shift current BPVE, mono- and bilayer structures of $3R$ and $2H$ $\alpha \text{−}\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$ are considered in our calculations. It suggests that the in-plane polarization doesn't affect the shift current response of this material. In monolayer, a dominant shift current response of magnitude $750\mu \mathrm{A}/{\mathrm{V}}^2$ is obtained along the direction of out-of-plane polarization under uniform illumination of $zz$-polarized light at a photon energy of 4.16 eV. The doping engineering is further implemented to tune the shift current response to visible light. Bismuth (Bi) is used to substitute the indium element at the tetrahedral site thereby introducing more energy levels in the conduction band which importantly are contributed by $p$ orbitals of Bi and take part in the transition process. Consequently, a giant shift current of $1200\mu \mathrm{A}/{\mathrm{V}}^2$ is obtained at a photon energy of 2.98 eV. The present study would be an instrumental in understanding the shift current BPVE and would pave the path for designing efficient photovoltaic devices based on $\alpha \text{−}\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$ and similar material systems.

中文翻译：

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二维α-In2Se3中移位电流体光伏效应的第一性原理计算

移位电流是整体光伏效应（BPVE）中主要的直流电流响应，该效应是具有反转反转对称性的材料中的太阳能到电能的转换。尽管BPVE的指导原理是在材料中也缺乏反转对称性，这也导致了铁电性，但因此，人们期望在铁电材料中获得相当大的移位电流。在这项工作中，我们使用二维的第一原理计算移位电流$\alpha \text{-}\mathrm{一世}{\mathrm{ñ}}_2\mathrm{小号}{\mathrm{Ë}}_3$在室温下具有平面内和平面外极化。要了解平面内和平面外极化对移位电流BPVE的影响，请注意单层和双层结构$3\mathrm{[R}$ 和 $2H$ $\alpha \text{-}\mathrm{一世}{\mathrm{ñ}}_2\mathrm{小号}{\mathrm{Ë}}_3$在我们的计算中被考虑。这表明面内极化不会影响这种材料的移位电流响应。在单层中，显性的主要移位电流响应$750\mu \mathrm{一种}/{\mathrm{V}}^2$ 在均匀照射下沿面外极化方向获得 $žž$偏振光，光子能量为4.16 eV。进一步实施掺杂工程以调整对可见光的移位电流响应。铋（Bi）用于代替四面体位点上的铟元素，从而在导带中引入更多的能级，这主要是由$p$Bi的轨道并参与过渡过程。因此，巨大的移位电流为$1200\mu \mathrm{一种}/{\mathrm{V}}^2$在2.98 eV的光子能量下获得。本研究将有助于理解位移电流BPVE，并为设计基于光伏的高效光伏器件铺平道路。$\alpha \text{-}\mathrm{一世}{\mathrm{ñ}}_2\mathrm{小号}{\mathrm{Ë}}_3$ 和类似的材料系统。