The electronic and optical properties of Cs₂ Ti_1-xB_xI₆(B=Sn, Te, Se) with first principle method

Abstract

Lead-free halide perovskite is regarded as the most promising light-harvesting material for solar cells recently. In this work, the properties of Cs${}_2$Ti${}_{1-x}$B${}_x$I${}_6$ (B=Sn, Te, Se) were investigated with first principle method based on density functional theory. The results show that Cs${}_2$Ti${}_{1-x}$Sn${}_x$I${}_6$ is an excellent photoelectric material in the sunlight. When the doping concentration was over $50\mathrm{\%}$, Cs${}_2$Ti${}_{1-x}$Se${}_x$I${}_6$ and Cs${}_2$Ti${}_{1-x}$Te${}_x$I${}_6$ have direct–indirect band gap transition. The values of energy gap, density of states and optical absorption coefficients in the visible light region are well matched to each other. Optical results show that absorption peaks locate near 330 nm and have strong ultraviolet absorption capacity. Doping Sn results in the spectrum redshifts and the absorption peak drops. While the peak becomes greater with the increase of tellurium, and the spectrum has obvious blueshift. The spectrum trends of Cs${}_2$Ti${}_{1-x}$Se${}_x$I${}_6$ are more complicated. This work provides theoretical supports for the development of novel optoelectronic materials by means of partial substitution doping.

GRAPHICAL ABSTRACT

Keywords:

• Lead-free perovskites
• density functional theory
• direct–indirect band gap transition
• absorption coefficient

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Fundamental Research Funds for the Central Universities of Criminal Investigation Police University of China, under Grant No. D2019018, Technical Research Program of the Ministry of Public Security, under Grant No. 2021JSYJC23.