First-principles study on bromide-based 2D hybrid organic-inorganic halide perovskites for perovskite solar cells

• Published in: The Journal of physics and chemistry of solids 2025-04, Vol.199, p.112496, Article 112496
• Main Authors: Bagha, Ghazaleh, Samavati, katayoon, Naffakh-Moosavy, Homam, Matin, Laleh Farhang
• Format: Article
• Language: English
• Subjects: 3D/2D perovskite solar cells; Blocking electrons; Capping layer; Passivation of defects; Spacer cation
• ISSN: 0022-3697
• DOI: 10.1016/j.jpcs.2024.112496

In recent years, two-dimensional (2D) hybrid organic-inorganic halide perovskites (HOIPs) have attracted attention due to their superior chemical stability and optoelectronic properties compared to their three-dimensional (3D) counterparts. Recently, 2D-HOIP (CMA)2PbI4 (n = 1), with an organic spacer cation containing a flexible cyclohexyl ring, has been used as a capping layer, which improves chemical stability by increasing the hydrophobicity of the CMA (CMA is cyclohexane methylammonium (C₆H₁₁CH₂NH₃)) surface in 3D/2D perovskite solar cells (PSCs). On the other hand, replacing iodine (I) with bromine (Br) in the 2D-HOIP (CMA)2PbI4 (n = 1) capping layer can introduce novel optical and electrical properties while maintaining chemical stability in 3D/2D PSCs. In this paper, the electronic and optical properties of 2D-HOIPs have been studied theoretically. Here, we examined the structural, electronic, and optical properties of 2D-HOIP (CMA)2PbBr4 (n = 1) by density functional theory (DFT) calculation. The bandgap of 2D-HOIP (CMA)2PbBr₄ was calculated using the HSE06 + SOC scheme and compared to the PBE and PBE + SOC results. Accordingly, the band structure calculation of 2D-HOIP (CMA)2PbBr₄ showed a direct bandgap of 2.72 eV (with space group P21/c). Notably, with a decreasing atomic radius of halogens (from I to Br), the electrostatic force from the nucleus on valence shell electron increases, thus increasing the bandgap between the conduction and valence bands in (CMA)2PbBr4. Moreover, compared to (CMA)2PbI4, the carrier mobility calculation of (CMA)2PbBr4 indicated a reduced recombination rate and facilitated the extraction of charge carriers (holes) by reducing electron mobility and the increasing hole mobility, respectively. Based on the calculation of the molecular orbital energy levels of (CMA)2PbBr4, due to the reduction in recombination of charge carriers (electron-hole) at the perovskite/HTL interface (by increasing the open-circuit voltage (VOC)), electron blocking, and defect passivation (by increasing the lowest unoccupied molecular orbital (LUMO) level), and facilitating charge carrier extraction (by fine-tuning the energy levels between perovskite layer and HTL), (CMA)2PbBr4 capping layer can enhance the performance of 3D/2D perovskite-based PSCs. Finally, 2D-HOIP (CMA)2PbBr4 as a capping layer increases power conversion efficiency (PCE (%)) by over 15 % compared to (CMA)2PbI4 in 3D/2D PSCs. •The 2D-HOIP (CMA)2PbBr4 capping layer enhances the