KAgSe: A New Two-Dimensional Efficient Photovoltaic Material with Layer-Independent Behaviors.

Abstract

Recent advances in the development of two-dimensional (2D) materials have stimulated people's interest and enthusiasm to discover new kinds of 2D functional materials. In this paper, we propose a novel 2D layered semiconductor KAgSe using the first-principles calculation method, which displays excellent photovoltaic properties with proper direct band gap and significant carrier mobility. By evaluating the cohesive energy, vibrational phonon spectrum, and temporal evolution of the total energy at a high temperature of 500 K, the KAgSe monolayer is proved to be stable. Finite cleavage energy comparable to that of black phosphorus implies the feasibility of mechanical exfoliation of a KAgSe monolayer from the bulk. Layered KAgSe shows a ∼1.5 eV direct band gap, which is roughly independent of the number of layers. Remarkable optical absorption coefficients in the visible light region and significant carrier mobilities reveal a favorable application prospect of layered KAgSe in photovoltaic devices. Especially, the layer-independent optical absorption provides enormous convenience and less difficulty in experimental fabrication of photoelectronic devices which are based on finite layer KAgSe. To further explore the photovoltaic behaviors, the polarization angle-related photocurrent is evaluated for the KAgSe monolayer-based nanodevice by irradiating a beam of linearly polarized light to the scattering region. Moreover, large photon responsivity and external quantum efficiency are also obtained for the KAgSe monolayer.