Efficient 2D homojunction optoelectronics enabled by interfacial coupling

Two-dimensional (2D) semiconductors have emerged as leading candidates for next-generation optoelectronics. Their unique electronic band structures, governed by quantum confinement at atomic thicknesses, make them ideal for efficient light absorption and charge transport. However, the development of functional devices, such as solar cells and photodetectors, fundamentally requires a "junction": an interface between two regions with distinct electrical properties. While stacking disparate materials to form heterojunctions is a common approach, these interfaces are often plagued by lattice mismatch and discontinuous band alignments. These defects induce carrier scattering and efficiency-robbing traps that ultimately degrade performance.

In contrast, 2D homojunctions formed within a single material offer a superior alternative, providing perfect lattice matching and seamless carrier diffusion across the interface. Despite their potential, fabricating these junctions is notoriously difficult, usually requiring complex chemical doping or local electrostatic gating to define specific carrier-doping regions within a single crystal.

In this work, J. Xu et al. present an elegant solution for fabricating an efficient homojunction. By using molybdenum disulfide (MoS₂) as a representative 2D semiconductor, they placed half of a MoS₂ flake onto a chromium oxychloride (CrOCl) substrate while leaving the other half pristine. The homojunction is formed through a two-step electronic modification: first, the pristine MoS₂ is naturally highly n-doped (n⁺); second, interfacial charge transfer between MoS₂ and CrOCl reduces the electron density in the supported region, resulting in a lightly n-doped (n⁻) state. Since CrOCl is an insulator, it does not interfere with the electronic transport of the resulting lateral n⁺–n⁻ MoS₂ homojunction.

The electronic features of the n⁺ and n⁻ regions were directly characterized by micro-angle-resolved photoemission spectroscopy (micro-ARPES) at the Spectromicroscopy beamline of Elettra. Scanning photoemission microscopy (SPEM) imaging clearly distinguished the pristine MoS₂ and MoS₂/CrOCl regions, in accordance with the optical microscopy (Fig. 1a). The high-symmetry directions of MoS₂ were determined by 3D ARPES constant energy cuts (Fig. 1b). Along the Г–K direction, the valence band maximum (VBM) of pristine MoS₂ is located at the K valley at E-E_F = -2.0 eV. Given the ~2.1 eV electronic bandgap of MoS₂, this confirms its n⁺ doping nature. In contrast, the VBM of MoS₂ on CrOCl shifted to E-E_F = -1.8 eV, representing a 200 meV upward band shift due to interfacial charge transfer (Fig. 1c), which confirms the n⁻ characteristics of the MoS₂ in this region. Energy distribution curves (EDCs) at the Г and M points further confirm this band shift (Fig. 1d).

Figure 1: (a) Optical image and corresponding SPEM image. (b) Constant-energy cuts from the 3D ARPES maps. (c) Micro-ARPES spectra along the Γ–K direction. (d) EDCs extracted from the Γ and M points. (e) Photocurrent distribution and (f) photovoltaic performance of the lateral n⁺–n⁻ MoS₂ homojunction. Adapted from J. Xu et al., ACS Nano 20, 5034-5043 (2026), with permission from ACS Nano.

Based on this n⁺–n⁻ architecture, the resulting lateral MoS₂ homojunction device yielded remarkable optoelectronic performance. The homojunction functioned as a powerful rectifying diode, creating a robust built-in electric field essential for the separation of photo-generated charges; notably, the photocurrent was localized exclusively at the n⁺–n⁻ interface (Fig. 1e). Under 532 nm illumination, the device achieved a record-breaking open-circuit voltage (VOC) of 0.87 V, among the highest ever recorded for 2D-based photovoltaics (Fig. 1f). Furthermore, the n⁺–n⁻ MoS₂ homostructures exhibited a detectivity exceeding 10¹² Jones and a responsivity of 0.98 A/W without external bias, demonstrating both ultrahigh photovoltaic and self-powered photodetection capabilities.

These results establish a universal strategy not only for constructing lateral semiconductor homojunctions with perfect lattice matching, but also for developing high-performance, multifunctional devices that integrate efficient photovoltaic conversion and self-powered photodetection within a single van der Waals semiconductor platform.

Jiyuan Xu¹, Yinglun Sun², Gangqiang Zhou1, Jiajun Fang¹, Alexei Barinov³, Nitin Mallik4, Azzedine Bendounan⁴, Marino Marsi⁵, Zailan Zhang⁶, Yingchun Cheng² and Zhesheng Chen^1
1 School of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing, P. R. China
² School of Science, Yanshan University, Qinhuangdao, P. R. China
³ Elettra-Sincrotrone Trieste S.C.p.A., Trieste, Italy
⁴ Société Civile Synchrotron Soleil, L’Orme des Merisiers, Départementale 128, Saint-Aubin, France
⁵ Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, Orsay, France
⁶ School of Physics, Nanjing University of Science and Technology, Nanjing, P. R. China

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