Type-II GeAs/GaSe heterostructure as suitable candidate for solar power conversion efficiency

The structural, electronic and optical properties of GeAs and GaSe under monolayer (ML), bilayer (BL) and heterostructure (HS) configurations calculated within the framework of density functional theory are presented. The stability of all configurations was confirmed by calculating the binding energy and phonon dispersion curves. Among all considered configuration, HS4 with AB stacking is most stable configuration and was considered for in-depth investigation. The electronic band structure calculations reveal the nature of all systems with moderate gap magnitude. The GeAs/GaSe HS4 and HS1 are observed to have a type- II band alignment with gap magnitude of 0.98 eV (PBE) and 1.80 eV (HSE) and 1.04 eV (PBE) and 2.01 eV (HSE) respectively, which is favourable for the photovoltaic and photocatalytic applications. Following this, the optical response of the systems suggest enhancement in photon absorption for HS configuration as compared to its constituent MLs. Moreover, the indirect to direct bandgap transition is observed on imposing 2% of tensile strain on the HS. To sum-up, the moderate electronic bandgap with a type-II band alignment and optimal absorption profile of GeAs/GaSe HS result in benchmarking solar power conversion efficiency (PCE) at 4% tensile strain of 22.32% with HSE which is remarkable compared to previously reported two-dimensional (2D) HSs. The present study provides motivation to experimentally explore such 2D HSs for harvesting abundant, green and clean solar energy.