Intercalated architecture of Mg2AlXY5 monolayer with built-in potential difference and high-power-conversion efficiencies

Screening novel two-dimensional (2D) layered materials that combine high stability with strong power-conversion efficiency has attracted considerable attention owing to their promise in 2D optoelectronic devices. However, centrosymmetric structures are often not conducive to the separation of photogenerated-carriers. Therefore, we propose a strategy to design a non-centrosymmetric multi-atomic layer monolayer, namely, Mg₂AlXY₅ (X = Ga, In; Y = S, Se, Te) using first-principles calculations. The results demonstrate that these Mg₂AlXY₅ monolayers possess excellent structural stability and built-in potential difference, which can effectively promote the separation of photogenerated carriers. Moreover, most of them exhibit desirable direct band gaps and high electron mobilities (up to ∼10³ cm²V^-1s^-1), indicating optical absorption spanning the near-infrared to visible region. Interestingly, spin-orbit coupling (SOC) drives an indirect-to-direct band-gap transition in Mg₂AlGaTe₅ and Mg₂AlInTe₅ monolayers. In addition, the Mg₂AlGaSe₅ monolayer is an effective donor material, and the corresponding Mg₂AlGaSe₅/InSe type II heterostructure achieve outstanding power-conversion efficiencies of 18.64%.