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

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 Pb2+ defect of perovskites via Lewis acid-base coordination. The Br atoms of BIE-Br could also passivate uncoordinated Pb2+, 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.

Automated summary

In this study, two organic molecules were designed and synthesized to modify the perovskite films in order to improve the efficiency and long-term stability of perovskite solar cells. The modified devices showed higher power conversion efficiency and maintained their initial performance after long-term storage.