All-2D asymmetric self-powered photodetectors with ultra-fast photoresponse based on Gr/WSe₂/NbSe₂ van der Waals heterostructure

The rise of smart wearable devices has driven the demand for flexible, high-performance optoelectronic devices with low power and easy high-density integration. Emerging Two-dimensional (2D) materials offer promising solutions. However, the use of 3D metal in traditional 2D devices often leads to Fermi-level pinning, compromising device performance. 2D metallic materials, such as graphene and 2H-phase NbSe₂, present a new avenue for addressing this issue and constructing high-performance, low-power photodetectors. In this work, we designed an all-2D asymmetric contacts photodetector using Gr and NbSe₂ as electrodes for the 2D semiconductor WSe₂. The asymmetric Schottky barriers and built-in electric fields facilitated by this architecture resulted in outstanding photovoltaic characteristics and self-powered photodetection. Under zero bias, the device exhibited a responsivity of 287 mA/W, a specific detectivity of 5.3 × 10¹¹ Jones, and an external quantum efficiency of 88 %. It also demonstrated an ultra-high light on/off ratio (1.8 × 10⁵), ultra-fast photoresponse speeds (80/72 μs), broad-spectrum responsiveness (405–980 nm), and exceptional cycling stability. The applications of the Gr/WSe₂/NbSe₂ heterojunction in imaging and infrared optical communication have been explored, underscoring its significant potential. This work offers an idea to construct all-2D ultrathin optoelectronic devices.