Self-assembled 2D WSe 2 thin films for photoelectrochemical hydrogen production

Abstract

WSe 2 -a layered semiconductor that can be exfoliated into atomically thin two-dimensional sheets - offers promising characteristics for application in solar energy conversion. However, the lack of controllable, cost-effective methods to scalably fabricate homogeneous thin films currently limits practical application. Here we present a technique to prepare controlled thin films of 2D WSe 2 from dispersions of solvent-exfoliated few-layer flakes. Flake self-assembly at a liquid/liquid interface (formed exceptionally from two non-solvents for WSe 2) followed by substrate transfer affords large-area thin films with superior 2D flake alignment compared with traditional (liquid/air) self-assembly techniques. We further demonstrate, for the first time, solar-to-hydrogen conversion from solution-processed WSe 2 thin films. Bare photoelectrodes with a thickness of ca. 25nm exhibit sustained p-type photocurrent under simulated solar illumination, and up to 1.0mAcm -2 at 0V versus reversible hydrogen electrode with an added water reduction catalyst (Pt). The importance of the self-assembled morphology is established by photoelectrochemical and conductivity measurements.