Given its innate coupling with wavefunction geometry in solids and its potential to boost the solar energy conversion efficiency, the bulk photovoltaic effect (BPVE) has been of considerable interest in the past decade^{1,2,3,4,5,6,7,8,9,10,11,12,13,14}. Initially discovered and developed in ferroelectric oxide materials², the BPVE has now been explored in a wide range of emerging materials, such as Weyl semimetals^9,10, van der Waals nanomaterials^11,12,14, oxide superlattices¹⁵, halide perovskites¹⁶, organics¹⁷, bulk Rashba semiconductors¹⁸ and others. However, a feasible experimental approach to optimize the photovoltaic performance is lacking. Here we show that strain-induced polarization can significantly enhance the BPVE in non-centrosymmetric rhombohedral-type MoS₂ multilayer flakes (that is, 3R-MoS₂). This polarization-enhanced BPVE, termed the piezophotovoltaic effect, exhibits distinctive crystallographic orientation dependence, in that the enhancement mainly manifests in the armchair direction of the 3R-MoS₂ lattice while remaining largely intact in the zigzag direction. Moreover, the photocurrent increases by over two orders of magnitude when an in-plane tensile strain of ~0.2% is applied, rivalling that of state-of-the-art materials. This work unravels the potential of strain engineering in boosting the photovoltaic performance, which could potentially promote the exploration of novel photoelectric processes in strained two-dimensional layered materials and their van der Waals heterostructures.

鉴于其与固体中波函数几何的先天耦合及其提高太阳能转换效率的潜力，体光伏效应 (BPVE) 在过去十年中引起了广泛关注^{1,2,3,4,5,6,7， 8,9,10,11,12,13,14}。BPVE最初是在铁电氧化物材料²中发现和开发的，现在已经在各种新兴材料中进行了探索，例如 Weyl 半金属^9,10、范德华纳米材料^11,12,14、氧化物超晶格¹⁵、卤化物钙钛矿¹⁶、有机物¹⁷ , 散装 Rashba 半导体¹⁸和别的。然而，缺乏优化光伏性能的可行实验方法。在这里，我们表明应变诱导极化可以显着增强非中心对称菱面体型 MoS ₂多层薄片（即 3R-MoS ₂）中的 BPVE。这种偏振增强的 BPVE，称为压电光伏效应，表现出独特的晶体取向依赖性，因为增强主要体现在 3R-MoS _{2的扶手椅方向}格，同时在之字形方向上基本保持完整。此外，当施加约 0.2% 的面内拉伸应变时，光电流增加了两个数量级以上，可与最先进的材料相媲美。这项工作揭示了应变工程在提高光伏性能方面的潜力，这可能会促进在应变二维层状材料及其范德瓦尔斯异质结构中探索新型光电过程。