Photovoltaic properties of two-dimensional van der Waals heterostructure Cs₃<i>X</i>₂I₉/InSe (<i>X</i> = Bi, Sb)

Abstract

Two-dimensional semiconductor heterostructures have excellent physical properties such as high light absorption coefficients, large diffusion lengths, high carrier mobility rates, and tunable energy band structures, which have great potential in the field of optoelectronic devices. Therefore, designing 2D semiconductor van der Waals heterostructures is an effective strategy for realizing multifunctional microelectronic devices. In this paper, the 2D van der Waals heterostructure Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe of non-lead Perovskite Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt; and indium-tin InSe is constructed to avoid the toxicity and stability problems of lead-based Perovskites. The geometrical, electronic structure and optical properties were calculated based on the first-principles approach of density-functional theory. It is shown that the 2D Cs&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe and Cs&lt;sub&gt;3&lt;/sub&gt;Sb&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe heterostructures are of type II energy band arrangement and have band gaps of 1.61 eV and 1.19 eV, respectively, with high absorption coefficients in the visible and UV ranges of up to 5×105 cm-1. Based on calculations of the deformation potential theory and the hydrogen-like atom model, the 2D Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe heterostructures have a high exciton binding energy (~0.7 eV) and electron mobility rate (~700 cm&lt;sup&gt;2&lt;/sup&gt; V&lt;sup&gt;-1&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;). The higher light absorption coefficient, carrier mobility, and exciton energy make the 2D Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe heterostructures suitable for photoluminescent devices. However, the energy band structure based on the Shockley-Queisser limit and type II arrangement shows that the intrinsic photoelectric conversion efficiency (PCE) of the 2D Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe heterostructures is only about 1.4%, which is not suitable for photovoltaic solar energy. In addition, the modulation and its rule of biaxial strain on the photovoltaic properties of 2D Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe heterostructures were further investigated. The results show that biaxial strain can improve the visible absorption coefficient of 2D Cs&lt;sub&gt;3&lt;/sub&gt;X&lt;sub&gt;2&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt;/InSe heterostructures, but cannot effectively improve its energy band structure, and the PCE is only increased to 3.3% at -5% biaxial strain. The above study provides a theoretical basis for the future design of efficient 2D van der Waals optoelectronic devices.