Tiwari Rajender Prasad
Asia Pacific Center for Theoretical Physics, Pohang 37673, Republic of Korea.
J Phys Condens Matter. 2022 Aug 30;34(43). doi: 10.1088/1361-648X/ac8b50.
The ferroelectric Rashba semiconductors (FERSCs) are endowed with a unique combination of ferroelectricity and the spin degree of freedom, resulting in a long carrier lifetime and impressive bulk photovoltaic (BPV) efficiency that reached 25% in organometal halide perovskites. The BPV efficiency can be further improved by using low-dimensional ferroelectrics however, it is inhibited by the ferroelectric instability in low-dimensional perovskites and toxicity along with phase instability of the lead-halide perovskites. To address these challenges, the-GeTe could be of great importance which is the simplest known lead-free FERSC with an intrinsic layered structure. Therefore, in this work, we investigate the BPV properties of three- to two-dimensional van der Waals structures of-GeTe by calculating the shift current (SHC). We predict that the mono (1.56 Å) and bi-layers (5.44-6.14 Å)-GeTe with the buckled honeycomb structure are dynamically stable and possess the characteristic features of the bulk up to the nanoscale limit. The SHC of ∼70A Vis calculated in bulk α-GeTe which is 20 times larger than that obtained in organometal halides in the visible light. The SHC increases with decreasing the number of layers, reaching a maximum amplitude of ∼300A Vat 2.67 eV in the monolayer which is more than double that obtained in monolayer GeS. We find that the SHC in monolayer α-GeTe can be further enhanced and redshifted by applying a compressive strain; which is correlated with the strong absorption of the-polarized light, stimulated by the more delocalized porbital character of the density of states. Furthermore, in the bilayer structures, the magnitude of the SHC is sensitive to the layers' stacking arrangement and a maximum SHC (∼250A V) can be achieved with an AB-type stacking arrangement. Combining these results with the benefits of being environmental-friendly material makes-GeTe a good candidate for next-generation solar cells application.
铁电 Rashba 半导体（FERSCs）兼具铁电性和自旋自由度这一独特组合，从而具有较长的载流子寿命以及令人瞩目的体光伏（BPV）效率，在有机金属卤化物钙钛矿中该效率达到了 25%。然而，通过使用低维铁电体，BPV 效率可进一步提高，但它受到低维钙钛矿中铁电不稳定性以及铅卤化物钙钛矿的毒性和相不稳定性的抑制。为应对这些挑战，GeTe 可能至关重要，它是已知最简单的具有本征层状结构的无铅 FERSC。因此，在这项工作中，我们通过计算位移电流（SHC）来研究 GeTe 从三维到二维范德华结构的 BPV 特性。我们预测，具有褶皱蜂窝结构的单层（1.56 Å）和双层（5.44 - 6.14 Å）GeTe 是动态稳定的，并且在纳米尺度极限内都具有体材料的特征。在块状 α - GeTe 中计算出的 SHC 约为 70 A/V，这比可见光下有机金属卤化物中的 SHC 大 20 倍。SHC 随着层数的减少而增加，在单层中于 2.67 eV 处达到约 300 A/V 的最大幅度，这是单层 GeS 中 SHC 的两倍多。我们发现，通过施加压缩应变，单层 α - GeTe 中的 SHC 可以进一步增强并发生红移；这与态密度中更离域的 p 轨道特征所激发的对偏振光的强吸收相关。此外，在双层结构中，SHC 的大小对层的堆叠排列敏感，采用 AB 型堆叠排列可实现最大 SHC（约 250 A/V）。将这些结果与 GeTe 作为环境友好材料的优势相结合，使其成为下一代太阳能电池应用的良好候选材料。
