(566i) WS2-Induced Enhanced Optical Absorption and Efficiency in Graphene/Silicon Heterojunction Photovoltaic Cells

The 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 to a photojunction. In this report, we design a Schottky junction-based photovoltaic system with single-layer graphene atop n-type silicon (n-Si), which when interfaced directly with few-layers of tungsten disulfide (WS₂) with an architecture of WS₂-Graphene/n-Si via a bottom-up CVD synthesis strategy, enhanced its power conversion efficiency. Here, the WS₂ induced photon absorption, only one atom above the photo-junction enhanced short-circuit current density, and the reconfiguration of the energy band structure led effective built-in electric field induced charge carrier transport (enhanced open-circuit voltage, V_OC). Similar to 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/cm² in comparison to 0.52 mA/cm² 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 solar cell 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.