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 two-dimensional (2D) semiconductor van der Waals heterostructures is an effective strategy for realizing multifunctional microelectronic devices. In this work, the 2D van der Waals heterostructure Cs₃<i>X</i>₂I₉/InSe of non-lead Perovskite Cs₃<i>X</i>₂I₉ and indium-tin InSe is constructed to avoid the toxicity and stability problems of lead-based Perovskites. The geometry, electronic structure, and optical properties are calculated based on the first-principles approach of density-functional theory. It is shown that the 2D Cs₃Bi₂I₉/InSe and Cs₃Sb₂I₉/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 range and UV range reaching to 5×10⁵ cm^–1. The calculation results from the deformation potential theory and the hydrogen-like atom model show that the 2D Cs₃<i>X</i>₂I₉/InSe heterostructure has a high exciton binding energy (~0.7 eV) and electron mobility rate (~700 cm²/(V·s)). The higher light absorption coefficient, carrier mobility, and exciton energy make the 2D Cs₃<i>X</i>₂I₉/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 Cs₃<i>X</i>₂I₉/InSe heterostructure is only about 1.4%, which is not suitable for photovoltaic solar energy. In addition, the modulation and its effect of biaxial strain on the photovoltaic properties of 2D Cs₃<i>X</i>₂I₉/InSe heterostructures are further investigated. The results show that biaxial strain can improve the visible absorption coefficient of 2D Cs₃<i>X</i>₂I₉/InSe heterostructure, but cannot effectively improve its energy band structure, and the PCE only increases to 3.3% at –5% biaxial strain. The above study provides a theoretical basis for designing efficient 2D van der Waals optoelectronic devices in future.