Photovoltaic Device Based on Monolayer Compositionally Graded Transition Metal Dichalcogenide Alloy

Monolayer transition metal dichalcogenides (TMDCs) have been widely studied for the fabrication of photovoltaic devices with high energy conversion efficiencies for future ultrathin optoelectronic devices. To create efficient photovoltaic devices, in-plane heterostructures, whose composition can be artificially tailored by chemical vapor deposition, are a promising approach to form p-n junctions spontaneously. Although sharp in-plane heterostructures are typically employed, their narrow heterointerfaces are prone to defect sensitivity and thermal losses, which can significantly reduce device performance. In this study, we demonstrated that the spontaneous p-n junction devices fabricated based on chemically synthesized compositionally graded monolayer WS_{2 x}Se_{2(1- x )} alloys exhibited enhanced photoresponse performance. By conducting photocurrent and photoluminescence mappings, we revealed the correlation between the photocurrent generation behavior and local composition gradient. Moreover, the monolayer alloy device exhibited an open-circuit voltage as high as 0.66 V, highlighting the potential of a compositionally graded p-n junction for high-efficiency photovoltaic devices. Our study presents a new approach for the development of efficient TMDC-based optoelectronic devices.