Multifunctional passivation strategy based on tetraoctylammonium bromide for efficient inverted perovskite solar cells

Highlights: • Tetraoctylammonium bromide is introduced to the perovskite films to passivate the defects of the films. • Inverted PSCs based on the modified films with a power conversion efficiency of 21.47% is achieved. • Device stability has also been greatly improved. • This strategy is based on post-treatment, which does not affect the perovskite film growth. Inverted perovskite solar cells (PSCs) have significant potential in large-scale production due to their low cost and low-temperature process-ability. Nevertheless, the efficiency of the inverted PSCs suffers from non-ideal light-harvesting, surface recombination, and charge extraction loss. Here, tetraoctylammonium bromide (TOAB) is introduced by a post-treatment strategy to address these challenges. The film properties and the corresponding device performance are systemically studied. The results show that TOAB molecules distribute throughout the perovskite films and thus effectively passivate the trap states at grain boundaries (GBs) and surface. The built-in electrical field (V_bi) of the devices and hydrophobic properties of the perovskite films are enhanced by TOAB molecular arrangement at the perovskite surface. Moreover, the light-harvesting efficiency is also improved via the redistribution of the light field in the PSCs. Benefiting from trap sates passivation, enhanced V_bi and light-harvesting, the champion power conversion efficiency (PCE) of 21.47% is achieved, which is among the reported high efficiencies for inverted PSCs. In addition, device stability has been greatly improved. The PCE of PSCs treated by TOAB can retain 81% of its initial value after 264 h in the air and can retain 94% of its initial value after 71 days in N₂. This work represents a novel passivation strategy by post-treatment method without disturbing the perovskite film growth to understand the sole defect effects on the device performance of PSCs.