Comparative Analysis of Thiophene-Based Interlayer Cations for Enhanced Performance in 2D Ruddlesden–Popper Perovskite Solar Cells

2D Ruddlesden–Popper (RP) perovskites have appeared as a promising prospective material owing to their tunable optoelectronic peculiarities and structural stability. The choice of interlayer cations greatly influences the performance of the 2D RP perovskites. In this study, through theoretical calculations and experimental investigation, we demonstrate the intrinsic and device performance differences between two perovskites based on cations of thiophenemethylamine (TMA) and thiopheneethylamine (TEA). Using density functional theory (DFT) calculations, it exposes that as compared to (TMA) 2 PbI 4, (TEA) 2 PbI 4 exhibits more pronounced distortion of [PbI 6 ] 4– units and possesses a wider band gap and larger effective mass. The experimental results on the TMA- and TEA-based 2D perovskites further show that when TEA is used as the interlayer cation, the crystallization process tends to form more low- n phases, which hinder charge transfer and decrease light harvesting. On the other hand, when TMA is used as the interlayer cation, excessive low- n phases are not observed, and the thin film exhibits excellent quality with significantly improved electron mobility. The (TMA) 2 (FA) n −1 Pb n I 3 n +1 ( n = 5) perovskite device shows a remarkable conversion efficiency of 16.56%, much higher than that of TEA-based devices (PCE = 2.58%). Moreover, the unencapsulated devices based on TMA were able to maintain 88% of their initial efficiency even after being exposed to the environment (RT, RH = 30 ± 5%) for a duration of 1080 h. These findings provide important insights into the differences between thiophene-based cations and the selection of organic interlayer cations for 2D RP perovskite solar cells.