Direct synthesis of two-dimensional MoS2 on p-type Si and application to solar hydrogen production

Abstract

Transition metal dichalcogenides (TMDs) are promising two-dimensional (2D) materials, and MoS₂ has been specifically utilized in electronic devices and integrated circuits. However, the direct synthesis of MoS₂ on traditional semiconductors, such as silicon, remains challenging due to the hydrophobic surface of nonoxide wafers (e.g., Si, GaAs, and InP). Herein, a novel, facile, reliable, and one-step method for the direct synthesis of single-crystal MoS₂ on a p-Si wafer via hybrid thermolysis is proposed. To demonstrate the applicability of the proposed method, a MoS₂/p-Si heterojunction was fabricated and used for solar-driven hydrogen production. The as-fabricated n-MoS₂/p-Si heterojunction exhibited a benchmark current density of −13.5 ± 1 mA/cm² at 0 V and an onset potential of +0.02 V. This method reliably and efficiently produced high-quality MoS₂ crystals on a wafer scale and is sufficiently simple to overcome the challenges associated with previous approaches. The method developed herein represents a tremendous advancement in the fabrication of 2D electronic devices.

2D semiconductors: Taming unruly crystals for green energy

Solar panels that catalyze the splitting of water into hydrogen fuel and oxygen can now be fabricated using a simple deposition process. Interfaces between two-dimensional molybdenum disulfide (2D-MoS₂) and electron-poor silicon can split water using light, but only when the naturally random crystallization patterns of 2D-MoS₂ are inhibited. Researchers led by Ho Won Jang from Seoul National University and Soo Young Kim at Chung-Ang University, Seoul, have improved uniformity in this ultrathin material by initially coating silicon wafers with a molybdenum oxide precursor that adheres in smooth layers. By depositing a second, sulfur-rich coating and then heating the sample, the team produced uniform 2D-MoS₂/silicon junctions down to 10-nanometer scales. The transparent device maintained a water-splitting photocurrent for over forty hours without degradation, thanks to the corrosion-resistant nature of high-quality 2D-MoS₂ crystals.