Theoretical Designs of Photoresponsive Energy-Storage Materials Based on Attachment of π-Conjugated Molecules onto Sulfur-Doped Graphene

Abstract

Introducing heteroatom active sites and functional units is essential for achieving high-performance graphene in potential applications of optoelectronic devices and sustainable solar-heat energy conversion/storage. Density functional theory calculations with long-range van der Waals effects (vdW-DF2) were performed to study the electronic structures and energy storage/release of graphene through sulfur (S)-doping and physisorption of π-conjugated photoresponsive molecules, trans/cis-azobenzene (AB) derivatives with an electron-donating substituent group and trans/cis-stilbene (ST), respectively. With the increase of the S-doping concentration from 0.4 to 0.8 atom/nm2, the band gap of graphene exhibits the enhanced metallic characteristics with a direct-to-indirect transition. Although AB and ST molecules have different unsaturated bridge bonds, −N═N– versus −CH═CH–, physisorption of these two photoresponsive molecules onto the graphene can both broaden the band gap to about 0.02 eV, as a result of the π–...