Janus β-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting

Abstract

Highly efficient, environmentally friendly and renewable sources of energy are of great need today to combat increasing energy demands and environmental pollution. In this work, we have investigated the novel 2D allotropes, i.e., β-Te₂X (X = S, Se), using first-principles calculations and study their potential applications in light harvesting devices. Both the monolayers possess high stability and semiconducting nature with an indirect band gap. The high carrier mobilities and excellent optical absorption of these monolayers make them potential candidates for solar conversion applications. We have proposed the type-II heterojunction solar cells and calculated their power conversion efficiencies (PCEs). The small conduction band offset and appropriate band gap of donor material in the case of β-Te₂S(S-Side)/α-Te₂S(Te-Side) heterojunction results in a PCE of ∼21%. In addition, the band alignments of these monolayers properly engulf the redox potentials of water. The overpotentials required to trigger hydrogen reduction (HER) and water oxidation (OER) half reactions reveal that HER and OER preferred acidic and neutral media, respectively. The calculated solar-to-hydrogen (STH) efficiencies of β-Te₂S (β-Te₂Se) monolayers turn out to be ∼13% (∼12%), respectively, which implies their practical applications in water splitting. Thus, our work provides strong evidence regarding the potential applications of these materials in the field of light harvesting devices.