Synergistic modification of benzimidazole and bromohexyl for highly efficient and stable perovskite solar cells

As nitrogen-rich adducts, both 1H-benzimidazole (BIE-H) and 1-(6-bromohexyl)-1H-benzimidazole (BIE-Br) could sufficiently passivate the unsaturated Pb 2+ defect of perovskites. Notably, the Br atoms of BIE-Br not only further promote the quality of the perovskite film, but also participate in the lattice restructuring of perovskite, which suppresses the non-radiative recombination of charge carriers, enlarges the band gap of perovskite and improves the energy level match of PSC. Furthermore, the presence of hydrophobic alkyl chains could protect the active layer from moisture erosion. Eventually, the BIE-Br modified PSC delivers a champion efficiency of 20.47% along with excellent operational stability. • 1. Nitrogen-rich adducts possess the tremendous potential to passivate unsaturated Pb 2+ defect in perovskites via Lewis acid-base coordination. • 2. The Br atoms of BIE-Br can not only further passivate the traps in perovskite, but also participate in the lattice restructuring of perovskite. • 3. The presence of hydrophobic alkyl chains could effectively protect the active layer from moisture erosion. • 4. The synergistic modification of benzimidazole and bromohexyl promoted the efficiency and stability of MAPbI 3 -based PSCs. High efficiency and long-term durability are two crucial factors for commercialization application of perovskite solar cells (PSCs). In this paper, we designed and fabricated two organic molecules to modify perovskite films. As nitrogen-rich adducts, both C−N and C=N groups in 1H-benzimidazole (BIE-H) and 1-(6-bromohexyl)-1H-benzimidazole (BIE-Br) possess the tremendous potential to passivate unsaturated Pb 2+ defect of perovskites via Lewis acid-base coordination. The Br atoms of BIE-Br could also passivate uncoordinated Pb 2+ , improving perovskite film quality and inhibiting non-radiative recombination of charge carriers. Moreover, Br - ions in BIE-Br could participate in the lattice restructuring of perovskite, which enlarges the band gap of perovskite and improves the energy level match of device, contributing to the decrease of energy losses during charge migration. Furthermore, the presence of hydrophobic alkyl chains could protect the active layer from moisture erosion, which enhances the durability of PSCs. As a result, the PCE of BIE-Br modified device reaches to 20.47%, much higher than those of the control and BIE-H treated PSCs, with efficiencies of 18.98% and 19.74%, respectively. The BIE-Br modified device also exhibits the significant long-term stability without any encapsulation, which maintains 78% of its initial PCE after 600 h storage under ambient conditions.