First-principles calculations of the effect of vacancy defects on the optoelectronic and mechanical properties of the double perovskite Cs₂NaInCl₆

Abstract Cs 2 NaInCl 6 have become a hot research topic in perovskite optoelectronic materials. However, there is no research on the vacancy properties of Cs 2 NaInCl 6 at present. Herein, using density functional theory-based first-principles calculations, the impact of Cs, Na, In, and Cl single vacancies on the microstructure, electronic, optical, and mechanical properties of the double perovskite Cs 2 NaInCl 6 were investigated. The research shows that the presence of vacancy defects leads to distortion of the Cs 2 NaInCl 6 double perovskite structure and an increase in the unit cell volume. Cs vacancy (V Cs ) and Na vacancy (V Na ) cause an increased band gap for Cs 2 NaInCl 6 , by 2.92 eV and 3.1 eV respectively, without changing the characteristics of the initial direct band gap; V In and V Cl cause the intrinsic semiconductor Cs 2 NaInCl 6 transform into p-type and n-type semiconductors, respectively, altering the conductivity of Cs 2 NaInCl 6 . In terms of optical properties, different vacancy defect systems exhibit different absorption abilities in the visible and ultraviolet light ranges. The defect system overall improves light absorption in the low energy region, and as the incident photon energy increases, the material exhibits the best optical performance at around 15 eV. In addition, it is found that V Cs , V Na , and V In caused blue shift in the absorption edge of Cs 2 NaInCl 6 , while V Cl caused red shift in the absorption edge. In terms of mechanical properties, defects cause varying degrees of reduction in Young’s modulus (E), shear modulus (G), and bulk modulus (B) of Cs 2 NaInCl 6 , which to some extent alters the mechanical properties of Cs 2 NaInCl 6 . These research results provide theoretical guidance for understanding the influence of vacancies on the properties of Cs 2 NaInCl 6 double perovskite and optimizing the performance of perovskite optoelectronic devices, and they also enhance its applications in photovoltaic cells, optoelectronic sensors, and other optoelectronic coupling devices.