Mixed-ligand ZIF-doped perovskite films toward damp-heat-stable solar cells

Perovskite solar cells (PSCs) are susceptible to environmental factors such as humidity and heat. Here, a mixed-ligand zeolitic imidazolate framework (ML-ZIF) synthesized by partially replacing the 2-methylimidazole (2-MIM) ligand in ZIF-8 with 2-mercaptoimidazole (2-MeIM) is introduced into a perovskite film as a multifunctional additive, which simultaneously modulates the crystallization of perovskite, passivates the bulk phase defects and enhances the damp-heat stability of the devices. In particular, the thiol groups in 2-MeIM strongly coordinate with undercoordinated Pb²⁺ ions at grain boundaries, effectively reducing the density of non-radiative recombination centers. Finally, the optimal ML-ZIF doped PSCs yield a high power conversion efficiency (PCE) of 24.12%, outperforming the control device (21.52%). The enhanced hydrophobicity and thermal conductivity imparted by ML-ZIF doping enable the devices to retain over 90% of their initial PCE after 700 hours at 65% relative humidity and 200 hours at 80 °C, respectively. Consequently, the incorporation of ML-ZIF presents a promising strategy to concurrently address the efficiency and stability challenges, thereby advancing the commercial prospects of PSCs.