High-performance, self-powered photodetectors based on vertically stacked van der Waals heterostructures toward bifacial photovoltaics

Self-powered photodetectors represent a transformative technology for next-generation wearable devices, particularly in environmental sensing and health monitoring applications. While significant progress has been made in this field, bifacial self-powered photodetectors utilizing vertically stacked van der Waals heterostructures remain largely unexplored. Here, we demonstrate an advancement in bifacial self-powered photodetectors through the innovative integration of a MoS2/WSe2 heterostructure as the photosensitive medium with transparent indium tin oxide and single-walled carbon nanotube (SWCNT) film electrodes in a vertical architecture. These photodetectors exhibit exceptional photodetection capabilities, ultrafast response speeds, and remarkable stability. Operating in photovoltaic mode, the photodetector achieves a notable open-circuit voltage of 0.52 V and a power conversion efficiency of 3.89 %, positioning it among the top-performing 2D materialbased photovoltaics reported to date. The exceptional bifacial functionality is evidenced by a near-unity bifacial factor of 98.5 %, demonstrating nearly equivalent power generation from both front and rear illumination. Furthermore, the photodetector delivers outstanding broadband photodetection performance across visible to near-infrared wavelengths, achieving a peak detectivity of 2.4 x 109 Jones under 840 nm laser illumination. This work not only establishes a scalable fabrication paradigm for wafer-scale flexible optoelectronics but also provides a fundamental framework for the development of advanced bifacial optoelectronics based on 2D materials.