WS2-induced enhanced optical absorption and efficiency in graphene/silicon heterojunction photovoltaic cells

Abstract

Van Hove singularity (VHS) induced enhancement of visible-frequency absorption in atomically-thin two-dimensional (2D) crystals provides an opportunity for improved light management in photovoltaics; however, it requires the 2D nanomaterial to be in close vicinity of a photojunction. In this report, we design a Schottky junction-based photovoltaic system with single-layer graphene atop n-type silicon (n-Si), which is interfaced directly with a few layers of tungsten disulfide (WS₂) via a bottom-up CVD synthesis strategy. An enhanced power conversion efficiency in the architecture of WS₂-graphene/n-Si is observed compared to graphene/n-Si. Here, the WS₂ induced photon absorption, with only three atoms above the photo-junction, enhanced the short-circuit current density (J_sc), and the reconfiguration of the energy band structure led to effective built-in electric field induced charge carrier transport (enhanced open-circuit voltage (V_oc)). Similar to a graphene/n-Si Schottky junction, the WS₂-graphene/n-Si double junction exhibited non-linear current density–voltage (J–V) characteristics with a 4-fold increase in J_sc (2.28 mA cm⁻² in comparison with 0.52 mA cm⁻² for graphene/n-Si) and 40% increase in the V_oc (184 mV compared to 130 mV for graphene/n-Si) with a 6-fold increase in the photovoltaic power conversion efficiency. Futuristically, we envision an evolution in 2D heterojunctions with sharp transitions in properties within a few nanometers enabling control on optical absorption, carrier distribution, and band structure for applications including tandem photovoltaic cells and 2D optoelectronic circuit-switches.