Tunable WSe2/WS2 van der Waals heterojunction for self-powered photodetector and photovoltaics

Abstract Two-dimensional semiconductors have emerged as promising candidates for next-generation optoelectronics due to their excellent carrier transport and strong light-matter interaction. Meanwhile, the feasibility of arbitrary van der Waals integration enables the construction of devices with designable interface properties. In this work, WSe2/WS2 heterostructures with type-II band alignment were fabricated for high-performance self-powered photodetector and photovoltaics. Due to the ambipolar nature of WSe2, the junction property could be efficiently modulated with electrostatic doping. Under optimized gate voltage and 532 nm laser illumination, the heterojunction yields a high open-circuit voltage of 0.58 V, the power conversion efficiency of 2.4%, and external quantum efficiency of 50.2%. The modulation of the photovoltaic response is demonstrated to be a combined effect of quasi-Fermi level tuning at the interface and channel conductivity change. Moreover, the diode exhibits spectral photoresponse from visible to the near-infrared region when it functions as a self-powered photodetector. The photoresponsivity reaches 216 mA/W and the rise and fall time are 80 μs and 90 μs, respectively. This work not only advances our fundamental understanding of device physics in van der Waals solar cells but also uncovers the great potential applications of WSe2/WS2 heterojunction in solar-energy conversion and photodetectors.