Unveiling intrinsic bulk photovoltaic effect in atomically thin ReS2

  The bulk photovoltaic effect (BPVE) is a nonlinear photocurrent that arises in non-centrosymmetric crystals when exposed to light [1]. It is an intrinsic property of the material, distinct from extrinsic effects like interfacial pn junctions or Schottky barriers. The BPVE manifests as a quadratic response to the incoming electric field or light polarization, offering a promising avenue for surpassing the efficiency limitations of conventional solar cells [2].   A key challenge in studying the BPVE lies in isolating the real intrinsic signal from other extrinsic, first-order photocurrents that can arise at different interfaces within a device. These extrinsic contributions can mask the intrinsic BPVE, making it difficult to accurately assess its performance.   To address this challenge, we fabricate high-quality, lateral ReS2 devices with minimal contact resistance, providing an optimal platform for isolation of the intrinsic BPVE signal [3]. Our devices exhibit large bulk photovoltaic performance with intrinsic responsivities of ~1 mA/W in the visible range, without the need for external tuning knobs such as strain engineering. Our experimental findings are supported by theoretical calculations. Furthermore, our approach can be extrapolated to investigate the intrinsic BPVE in other non-centrosymmetric van der Waals materials, paving the way for a new generation of efficient light-harvesting devices.   References   1. T. Morimoto, et al. Topological nature of nonlinear optical effects in solids. Science Adv. 2, e1501524 (2016). 2. W. Shockley, et al. Detailed balance limit of efficiency of p‐n junction solar cells. J. Appl. Phys. 32, 510 (1961). 3. M. Ramos, et al. Unveiling intrinsic bulk photovoltaic effect in atomically thin ReS2. Submitted to Nano Letters (2024).