Activate whole-body passivation ability of small isomeric D-π-A molecules via amino position effect to improve the photovoltaic performance of perovskite solar cells

Passivating defects via organic molecule additives is one of important approaches to achieve high-efficient and stable perovskite solar cells (PSCs). To unveil the influence mechanism of intermolecular charge transfer caused by molecular structure on defect passivation is imperative for activating whole-body passivation ability of molecules. Small isomeric D-π-A molecules of methyl 2-amino-4-methoxybenzoate (M2A4M) and methyl 3-amino-4-methoxybenzoate (M3A4M) with multiple coordination sites provide us a desired research object to unveil how the intermolecular charge transfer caused by amino group position activate the passivation ability of molecule to boost the photovoltaic performance of PSCs. The results show that the ortho amino group within M2A4M is beneficial for part of electrons at –CH3O transferring to the methoxy and amino groups through benzene ring to activate their whole-body coordination ability with MA+ or Pb related defects. In detail, a unique bidentate chelating bond between M2A4M and uncoordinated Pb2+ ions in the perovskite can be formed due to a good distance match between functional groups on M2A4M and adjacent octahedral voids on the perovskite caused by ortho amino group, which provides the stronger adsorption capacity to anchor M2A4M on the perovskite to passivate internal defects. Moreover, the formation of hydrogen bond between activated methoxy group in M2A4M and NH3+ in the perovskite can inhibit the ion migration to improve the stability of PSCs. As a result, the champion MAPbI3 based PSCs treated with M2A4M achieves the highest photoelectric conversion efficiency of 21.51 % with an open circuit voltage of 1.16 V. This work provides a novel concept for designing appropriate molecular structure of additives with whole-body defect passivation ability, which will prompt the further development of perovskite-based photoelectric devices.