Isomers with synergistic effects of multiple functional groups enabling high-performance perovskite solar cells

The organics containing multiple Lewis base groups are commonly used as additives to build high-quality perovskite film to improve the performance of perovskite solar cells (PSCs). However, the relationship between the synergistic effects of the multifunctional groups induced by the molecular configuration of the additives and their effect remains to be probed. Herein, the isomeric additives of 2-amino-5-iodobenzoic acid (O-IA) and 4-amino-3-iodobenzoic acid (P-IA) are selected to in detail explore the impact of molecular conformation on their modulation of perovskite film quality. Theoretical and experimental analyses reveal that compared to the adsorption effect formed by the para-position –C=O and –NH₂ groups in P-IA with the adjacent lead ions in the perovskite lattice, the multidentate chelating constituted by the ortho-position –C=O and –NH₂ groups in O-IA with the single lead ions results in its a stronger bonding with the perovskite precursor and the (1 1 0) plane of perovskite, which modulates the crystallization and preferential growth of the perovskite film. Additionally, the stronger intermolecular interactions of O-IA and its bonding with perovskite than P-IA more effectively release the strain of perovskite film. Therefore, the O-IA-treated perovskite film exhibits substantially enhanced oriented crystallization, reduced residual strain and defect states, and improved energy level matching. As a result, the unencapsulated air-processed carbon-based PSCs with O-IA achieve a champion power conversion efficiency of 17.50% and superior stability after 480 h of aging in air at 50 °C, 20% relative humidity (RH) and at 25 °C, 85% RH.