Multiple functional groups synergistically improve the performance of inverted planar perovskite solar cells

Highlights: • 1-propionate-4-amino-1,2,4-triazolium tetrafluoroborate is designed as additive. • Strong interaction between additive and perovskite enables a high-quality film. • The PCE of optimized device is up to 21.35%, along with the excellent stability. Numerous defects may occur during the preparation of perovskite films, and these defects obstruct the charge transfer and accelerate the decomposition of films. Herein, the 1-propionate-4-amino-1,2,4-triazolium tetrafluoroborate (PATMBF₄) is employed as a multifunctional additive for caesium (Cs), methylammonium (MA) and formamidinium (FA) triple-cation-based perovskites (CsFAMA) to prepare inverted planar solar cells. The amino group (-NH₂) in PATM⁺ can donate free electron pair to form a Pb-N coordination bond with perovskite, which can not only regulate crystal growth, but also decrease the generation of charge recombination centers to make charge transfer more effective. The hydrogen bond formed between the carbonyl group (CO) contained in PATM⁺ and FA⁺ (O···H-N) restrains the migration of FA⁺ to the film surface, thus retarding the decomposition of film. Hence, the photoelectric conversion efficiency (PCE) of the champion device is as high as 21.35%. In addition, the PCE can sustain over 85% after exposure to air for 4000 h with a relative humidity of 40 ± 5%, and only drops by 10% in the case of 85 °C more than 1000 h (N₂). It can retain 90% of PCE under the full-spectrum sunlight for 800 h (N₂).