Manipulation of cation combinations and configurations of halide double perovskites for solar cell absorbers

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2018, Vol.6 (4), p.189-1815
• Main Authors: Zhang, Peng, Yang, Jingxiu, Wei, Su-Huai
• Format: Article
• Language: English
• Subjects: Absorbers; Cations; Density functional theory; First principles; Lead; Lead free; Metal ions; Occupation; Perovskites; Photovoltaic cells; Solar cells
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c7ta09713a

Pb-free halide double perovskites, A 2 B + B 3+ X 6 (A = Cs, B + /B 3+ = metal cation, and X = halogen anion), have been proposed to replace hybrid halide perovskites ( e.g. , CH 3 NH 3 PbI 3 ) as stable Pb-free materials for high efficiency solar cell absorbers. Here, using first-principles density functional theory calculations and symmetry analysis we show that the overall electronic properties of A 2 B + B 3+ X 6 depend strongly on the atomic orbitals and site occupation of the B + and B 3+ cations. For ordered A 2 B + B 3+ X 6 compounds, in order to have a direct band gap with allowed optical transitions, both of the B + and B 3+ cations should possess the lone-pair s state. Thus, only the A 2 B IIIA + B VA 3+ X 6 family of compounds satisfies this criterion. On the other hand, we reveal that the electronic structures of A 2 B + B 3+ X 6 can be greatly tuned by controlling the site occupation ordering parameter of the B + and B 3+ cations. Compared to their ordered counterparts, the band gaps of disordered A 2 B + B 3+ X 6 alloys can be reduced significantly and the band gap character can be switched from indirect to direct, which greatly expanded the possible candidates for solar cell applications. Our results thus set a new direction and guidelines for the design of Pb-free halide double perovskites for solar cells. The overall electronic properties of double perovskite A 2 B + B 3+ X 6 (A = Cs, B + /B 3+ = metal cation, and X = halogen anion) as function of atomic orbitals and site occupation of the B + and B 3+ cations are studied by using first-principles calculations and symmetry analysis for high efficiency solar cell absorbers.