Tunable long-lived exciton lifetime in single-layer two-dimensional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>LiAlTe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Hao Dong, Jinfeng Zhao, Huan Yang, Yujun Zheng
Abstract
In two-dimensional (2D) materials, Coulomb interactions induce large binding energies of excitons, which are detrimental to the charge separations and hence crucial to photovoltaic performance. Here, we elucidate that this drawback can be well restrained in 2D materials with an intrinsic polarization field. Based on first-principles calculations combined with nonadiabatic molecular dynamics, we propose an embodied example of a ${\mathrm{LiAlTe}}_{2}$ quadruple layer. Due to the inherent electrical polarization field in 2D ${\mathrm{LiAlTe}}_{2}$, the electron and hole wave functions are separated into opposite atomic layers similar to the case of heterostructures, reducing the undesired Coulomb interactions and contributing to the small binding energy of excitons. Through modeling and recording the excited-state dynamics, we reveal that 2D ${\mathrm{LiAlTe}}_{2}$ harbors an ultralong lifetime of excitons of about 1.69 ns, a recombination time that is similar to that found in type-II van der Waals heterostructures and superior to hitherto known $2\mathrm{D}$ photovoltaic components. Furthermore, the effect of strain on the electron-hole recombination is studied quantitatively. Our findings not only provide a compelling candidate for applications in wearable and flexible thin-film solar cells, but also suggest one of the possible ways to design the thin-film solar cells.