Stable and efficient perovskite solar cells via hydrogen bonding and coordination

The instability of perovskite solar cells (PSCs) is primarily caused by the unavoidable ion migration in the perovskite layer. Ion migration and accumulation influence the properties of perovskite and functional layers, resulting in severely degraded device performance. Herein, we introduced an n-type, low optical gap-conjugated organic molecule (i.e., COTIC-4F or COTIC-4Cl) to serve as the perovskite photoactive layer in a perovskite precursor solution for broadening the near-infrared spectral response and enhancing the efficiency of PSCs. Various characterization studies have determined that COTIC-4F forms hydrogen bonds with perovskites, thereby remarkably enhancing the anchoring ability of MA(+), suppressing ion migration, and reducing photocurrent hysteresis. Meanwhile, the carbonyl (C=O) group of COTIC-4F and COTIC-4Cl can donate a lone electron pair to passivate the Pb trap, avoiding possible carrier recombination. The COTIC-4F- and COTIC-4Cl-treated perovskite films exhibit an optical response in the near-infrared region and an excellent morphology. Through ultraviolet photoelectron spectroscopy, it has been determined that COTIC-4F can facilitate more charge transfer than COTIC-4Cl, which results in a larger photocurrent from the PSCs. The PSCs of the COTIC-4F-treated perovskite films demonstrate a maximum power conversion efficiency of 21.72%. They exhibit a high fill factor of 82.02% and possess long-term stability under an air atmosphere.