A promising two-dimensional solar cell donor: Black arsenic-phosphorus monolayer with 1.54 eV direct bandgap and mobility exceeding 14,000 cm2 V-1 s-1

Excitonic solar cells (XSCs) have attracted tremendous attentions due to their high solar-to-electric power conversion efficiency (PCE). However, to further improve the PCE of XSC, finding an efficient donor material with both suitable direct bandgap and high carrier mobility is still a great challenge. Here, we report a black arsenic-phosphorus monolayer as highly efficient donor for XSCs based on first-principle calculations. Firstly, monolayer arsenic-phosphorus polymorphs with alpha, beta, gamma, delta, and epsilon phases were built, among which alpha-AsP and beta-AsP have been verified to be thermodynamically stable. Significantly, monolayer alpha-AsP possesses a direct bandgap with energy of 1.54 eV, which covers the main energy of solar spectrum. Moreover, its electronic mobility is as high as 14,380 cm(2) V-1 s(-1), which is much higher than silicon. These two crucial merits made it a promising candidate as donor materials for XSC device and the theoretical simulations demonstrate a maximum PCE of 22.1% for the primarily designed alpha-AsP/GaN XSC. Interestingly, the suitable electronic structure of oc-AsP enables a formation of perfect type-II semiconductor heterojunction with GaN, which will boost the separation and transport of photo generated carriers with the assistance of built-in field and high mobility. Particularly, alpha phase few-layer material of arsenic-phosphorus alloy has been experimentally synthesized recently, which paves the way for experimental realization of black arsenic-phosphorus monolayer donor. (C) 2016 Elsevier Ltd. All rights reserved.