# Photovoltaic Device Based on Monolayer Compositionally Graded Transition Metal Dichalcogenide Alloy

## TL;DR

A new photovoltaic device using a graded alloy of WS2 and Se2 shows improved performance due to a spontaneous p-n junction.

## Contribution

A new approach using compositionally graded monolayer alloys to create efficient p-n junctions in photovoltaic devices.

## Key findings

- Devices showed an open-circuit voltage of up to 0.66 V.
- Photocurrent generation correlated with local composition gradients.
- High gate tunability and notable performance were observed in the devices.

## Abstract

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 WS2

x
Se2(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.

Photovoltaic devices based on compositionally graded monolayer WS2

x
Se2(1‐

x

) alloys were fabricated and characterized. A spontaneous p‐n junction was formed inside the alloy region, and significant photocurrent was collected. The devices exhibited high gate tunability with a large open‐circuit voltage. The simple structure and notable performance of these photovoltaic devices indicate the potential of our new approach for exploiting efficient optoelectronics based on synthesized monolayer alloys.