Intercalated Architecture of the Ca 2 A 2 Z 5 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 Ca 2 A 2 Z 5 (A = Al and Ga and Z = S, Se, and Te) by first-principles calculations. Our results indicated that the energies of α 1 -phase Ca 2 A 2 Z 5 are slightly lower than those of experimentally synthesized α 3 -phase-like Ca 2 A 2 Z 5 monolayers with excellent structural stability. Moreover, the α 1 - and α 3 -phase Ca 2 A 2 Z 5 monolayers possess not only direct band gaps but also high electron mobilities (up to ∼10 3 cm 2 V -1 s -1 ), demonstrating an intriguing range of visible light absorption. Importantly, α 1 - and α 3 -phase Ca 2 Ga 2 Se 5 monolayers are good donor materials, and the corresponding Ca 2 Ga 2 Se 5 /ZrSe 2 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 Ca 2 A 2 Z 5 candidate monolayers for the application of high-performance solar cells.