Enhancing Luminescence Performance of Te-Substituted Cs₂SnCl₆ through Te–Te Distance Tuning and Strain Optimization

To achieve highly efficient luminescence with A2BX6-type tin(IV)-based metal halide perovskites, it is essential to overcome their parity-forbidden electronic transition characteristics. For Cs2SnCl6, Te substitution has been demonstrated as an effective strategy; however, its luminescence can be significantly reduced or even quenched under certain conditions. To uncover the microscopic mechanisms driving this behavior and optimize the luminescence performance of Te-substituted Cs2SnCl6, we conducted first-principles calculations to examine the effects of the Te–Te distance and strain conditions. Our findings reveal that the cosubstitution of Te atoms at two nearest-neighbor Sn positions induces significant octahedral distortion, energy band broadening, and an increase in the transition dipole moment, which collectively enhance luminescence performance. However, at high Te substitution concentrations, electron transitions are suppressed, resulting in luminescence quenching. In terms of mechanical strain, we found that uniaxial tensile strain improves luminescence performance, while uniaxial compressive strain and biaxial strain have a detrimental effect. These findings provide valuable insights into the luminescence mechanism of Te-substituted Cs2SnCl6 and may be applicable to other related tin halide perovskite materials, offering important guidance to optimize their luminescence properties for advanced optoelectronic applications.