Strain Engineering on the Optoelectronic Properties of CsPbI3 Halide Perovskites: Ab-Initio Investigation

We have studied the effects of uniaxial strain on the electronic and optical properties in CsPbI3 perovskite using density functional theory. The unstrained CsPbI3 has a band gap energy of 1.63 eV. We have applied a compressive and tensile strain (- 5% to 5%) in each of the three crystallographic directions independently. We have observed an anisotropic behavior in the variation of the band gap energy in the case of a tensile strain along the c-direction, where the band gap varies differently compared to the case of a tensile strain along the a- and b-directions. This unusual behavior appears up to a tensile strain of 3.5%, where the band gap energy reaches a value of 1.74 eV. The key factor of this atypical behavior was attributed to the distortion of the structure caused by the inclination of the PbI6 octahedral, the deviation of the Pb-I-Pb angle from the ideal angle of 180 degrees. Furthermore, through ab initio calculations, we found that CsPbI3 has several interesting optical properties related to the strain, remarkable optical absorption (about 10(5) cm(-1)), refractive index (2.25) and excellent optical conductivity. These properties make CsPbI3 a very promising candidate for Optoelectronics applications.