Intercalated Architecture\nof the Ca<sub>2</sub>A<sub>2</sub>Z<sub>5</sub> Monolayer with High\nElectron Mobilities and\nHigh Power Conversion Efficiencies

The exploration of novel two-dimensional (2D) materials\nwith a\ndirect band gap and high mobility has attracted huge attention due\nto their potential application in electronic and optoelectronic devices.\nHere, we propose a feasible way to construct multiatomic monolayer\nCa<sub>2</sub>A<sub>2</sub>Z<sub>5</sub> (A = Al and Ga and Z = S,\nSe, and Te) by first-principles calculations. Our results indicated\nthat the energies of α<sub>1</sub>-phase Ca<sub>2</sub>A<sub>2</sub>Z<sub>5</sub> are slightly lower than those of experimentally\nsynthesized α<sub>3</sub>-phase-like Ca<sub>2</sub>A<sub>2</sub>Z<sub>5</sub> monolayers with excellent structural stability. Moreover,\nthe α<sub>1</sub>- and α<sub>3</sub>-phase Ca<sub>2</sub>A<sub>2</sub>Z<sub>5</sub> monolayers possess not only direct band\ngaps but also high electron mobilities (up to ∼10<sup>3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>), demonstrating\nan intriguing range of visible light absorption. Importantly, α<sub>1</sub>- and α<sub>3</sub>-phase Ca<sub>2</sub>Ga<sub>2</sub>Se<sub>5</sub> monolayers are good donor materials, and the corresponding\nCa<sub>2</sub>Ga<sub>2</sub>Se<sub>5</sub>/ZrSe<sub>2</sub> type-II\nheterostructures exhibit desirable power conversion efficiencies of\n22.4% and 22.9%, respectively. Our findings provide a feasible way\nto explore new 2D materials and offer several Ca<sub>2</sub>A<sub>2</sub>Z<sub>5</sub> candidate monolayers for the application of\nhigh-performance solar cells.