Efficient charge separation and visible-light response in bilayer HfS2-based van der Waals heterostructures.

Xiaorui Chen,Hong Chen,Xukai Luo,Hongkuan Yuan,Junli Chang,Biao Wang

doi:10.1039/c8ra03047b

Abstract

Two-dimensional (2D) hafnium disulfide (HfS2) has been synthesized and is expected to be a promising candidate for photovoltaic applications, and at the same time the hexagonal BN sheet (h-BN) and graphene-like C3N4 sheet (g-C3N4) have also been fabricated and are expected to be applied in photocatalysis. In this work, we employ hybrid density functional theory to investigate HfS2-based van der Waals (vdW) heterojunctions for highly efficient photovoltaic and photocatalytic applications. HfS2/h-BN and HfS2/g-C3N4 heterostructures with direct bandgaps and efficient charge separation are both typical type-II semiconductors and have potential as photovoltaic structures for solar power. Moreover, compared with h-BN and g-C3N4 single-layers, HfS2/h-BN heterostructures with 6% tensile strain and HfS2/g-C3N4 heterostructures with 9% tensile strain have moderate bandgaps, whose optical absorption is obviously enhanced in the ultraviolet-visible (UV-VIS) light range and whose bandedges are suitable for photocatalytic water splitting. HfS2/h-BN heterostructures with 6% applied strain, being different from HfS2/g-C3N4 heterostructures with 9% strain, possess a direct bandgap and show complete separation of the photoinduced electron–hole pairs. Thus the HfS2/h-BN heterojunction with 6% strain has bright prospects for use in visible light photocatalytic water splitting to produce hydrogen.

Highlights

Since the discovery of graphene,[1] ultrathin 2D nanomaterials[2,3] have attracted widespread attention due to their peculiar properties and high utilization efficiency of speci c surface areas, which are of signi cance for potential applications such as photocatalysis
Because HfS2 is predominantly an ionic crystal with a moderate bandgap and a “two-dimensional” layered structure bonded by weak van der Waals forces,[9] it has been inspiring researchers to study its properties from bulk to monolayer.[10,11,12]
We mainly investigate whether the bilayer van der Waals (vdW) heterostructures with combined HfS2 and hexagonal BN sheet (h-BN) (g-C3N4) layers can form standard type-II heterojunctions, which are

Summary

Introduction

Since the discovery of graphene,[1] ultrathin 2D nanomaterials[2,3] have attracted widespread attention due to their peculiar properties and high utilization efficiency of speci c surface areas, which are of signi cance for potential applications such as photocatalysis. Because of the high cost and difficulty in manufacturing 2D heterojunctions in the laboratory, theoretical research is necessary to predict whether or not they can be used as catalysts for hydrogen evolution by water splitting.[26] the g-C3N4 and hexagonal boron nitride (h-BN) monolayers have become elementary slabs for vdW heterostructures.[27] Here, we mainly investigate whether the bilayer vdW heterostructures with combined HfS2 and h-BN (g-C3N4) layers can form standard type-II heterojunctions, which are. Paper deemed to be able to enhance the separation of electron–hole pairs Their band gaps and band edge positions, the effect of the biaxial strain, the density of states and optical absorption spectra are calculated by density functional theory

Computational method

Structural stability

Band structure and density of states

Charge transfer analysis

Optical properties

Conclusions