Identifying the Ground-State NP Sheet through a Global Structure Search in Two-Dimensional Space and Its Promising High-Efficiency Photovoltaic Properties

Recently fabricated two-dimensional (2D) black phosphorene (BP) is considered to be a promising optoelectronic sheet, but its applications are hindered by the poor stability in air. Thus, it is desirable to investigate other BP-like 2D materials, which may have improved stability, while preserving the exceptional electronic properties of BP. Herein, using an efficient structure search method, we predicted a novel 2D BP-like material, namely, a honeycomb NP sheet (α-NP). Remarkably, its few-layer α-NP sheets possess not only a tunable direct bandgap under in-plane strain but also high mobility (×104 cm2 V-1 s-1) and absorption coefficients (×105 cm-1). These advantageous characteristics endow the α-NP sheets as a very potential 2D material for efficient photovoltaic cell applications, as demonstrate by an estimated photovoltaic efficiency of ∼14%, when its thickness is at ∼1 μm. When combined with 2D MoTe2, it can provide a type-II heterojunction solar cell with a conversion efficiency up to ∼16%. We also proposed a feasible strategy for mechanical cleavage to prepare the α-NP sheets from its bulk NP compound. Once prepared, the α-NP sheets may offer superior photovoltaic properties and facilitate the development of solar cells and optoelectronic devices.