Molecular structure effects of passivation agents on the performance of perovskite solar cells

The performance of perovskite solar cells (PSCs) is affected by a non-radiative recombination process involving defects in the perovskite films. To tackle this challenge, herein, aryl sulfonates and alkyl sulfates with distinct molecular structures, specifically sodium benzenesulfonate (SBS) and sodium dodecyl sulfate (SDS), as additives to passivate the defects in the methyl ammonium lead iodide (MAPbI₃) perovskite films. This study examines the impact of the molecular structure of these additives on both the characteristics of the perovskite films and the performance of the PSCs. The results demonstrate that both SBS and SDS, which contain –S-O^- and Na⁺ ions in their structures, effectively increase the efficiency of PSCs. This improvement is attributed to the ability of these ions to interact with oppositely charged defects, leading to reduced trap densities in the perovskite films. Remarkably, SDS stands out with its long alkyl chain and a larger head group (C-O-S-O-) carrying a higher negative charge, showcasing superior defect passivation compared to SBS. The SBS molecule, on the other hand, features a phenyl group and a smaller head group (C-S-O-) with a reduced negative charge. This is primarily due to the significant role played by the phenyl ring in delocalizing the negative charge. As a result, the SDS-treated PSCs can achieve a remarkable champion power conversion efficiency of 20.70 %. Additionally, the contact angle of water on the SDS-treated perovskite films surpasses that on the SBS-treated film. This highlights an enhanced hydrophobic characteristic, ultimately bolstering the stability of SDS-treated PSCs.