Designing Double Perovskites with Organic Dications for Enhancing Stability and Photoelectrical Performance

Recently, the research on developing lead-free double-B-cation halide perovskites has attracted attention. However, Cs₂InBiCl₆, the most promising one, was shown to be thermodynamically unstable. To improve the stability, organic dication DiMA²⁺ (i. e., (CH₂NH₃)⁺(CH₂)₃(CH₂NH₃)⁺) is introduced to design the new double perovskite DiMAInBiX₆ (X=Cl, Br, and I) based on Cs₂InBiX₆ by replacing two Cs⁺ with a DiMA²⁺. Density functional theory calculations were performed to study the geometric and photoelectric properties of the newly designed materials. Unlike Cs₂InBiX₆, both DiMAInBiCl₆ and DiMAInBiBr₆ can exist stably against decompositions, indicating that the replacement of Cs⁺ by DiMA²⁺ will improve stability of double perovskites due to the staple effect. In addition, the replacement causes an increase in the band gaps of DiMAInBiX₆. Particularly, the calculated band gap of DiMAInBiBr₆ (1.31 eV) is close to the optimal value of single junction perovskite solar cell (PSC). Under ideal conditions, the PSC model constructed with DiMAInBiBr₆ performs the best in theoretical simulation. This work proposes DiMAInBiBr₆ as a promising light absorber of PSC, which has high stability and photoelectric performance. It also suggests that the replacement of Cs⁺ by DiMA²⁺ may serve as a rational and practical way to design new organic-inorganic hybrid double perovskites.