Intercalated Architecture of the Ca₂A₂Z₅ Monolayer with High Electron Mobilities and High Power Conversion Efficiencies

The exploration of novel two-dimensional (2D) materials with a direct band gap and high mobility has attracted huge attention due to their potential application in electronic and optoelectronic devices. Here, we propose a feasible way to construct multiatomic monolayer Ca₂A₂Z₅ (A = Al and Ga and Z = S, Se, and Te) by first-principles calculations. Our results indicated that the energies of α₁-phase Ca₂A₂Z₅ are slightly lower than those of experimentally synthesized α₃-phase-like Ca₂A₂Z₅ monolayers with excellent structural stability. Moreover, the α₁- and α₃-phase Ca₂A₂Z₅ monolayers possess not only direct band gaps but also high electron mobilities (up to ∼10³ cm² V^-1 s^-1), demonstrating an intriguing range of visible light absorption. Importantly, α₁- and α₃-phase Ca₂Ga₂Se₅ monolayers are good donor materials, and the corresponding Ca₂Ga₂Se₅/ZrSe₂ type-II heterostructures exhibit desirable power conversion efficiencies of 22.4% and 22.9%, respectively. Our findings provide a feasible way to explore new 2D materials and offer several Ca₂A₂Z₅ candidate monolayers for the application of high-performance solar cells.