Difluorine-substituent tailored roles of aromatic monoammonium cations on the perovskite surface

Aromatic monoammonium cations (AMCs) have been widely used to ameliorate the perovskite surface by interacting with defects or constructing low-dimensional perovskites, yet ignoring substituent effects on the working principle of AMCs. Here, we demonstrated that benzylammonium cation (BA) and difluorinated BA (DFBA) AMCs play different roles on the perovskite surface. BA can transform three-dimensional (3D) perovskite into two-dimensional (2D) ones on perovskite surface, but the 2D perovskites with random orientation impede charge extraction and increase nonradiative charge recombination. As a comparison, DFBA cannot form 2D perovskites, while directly interacting with the perovskite surface, simultaneously improving the contact between the perovskite and 2,2 ',7,7 '-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9 '- spirobifluorene (Spiro-OMeTAD) layer, promoting interfacial charge extraction, thus boosting the efficiency to 20.29 % and 24.02 % for (CH3NH3)PbI3 (MAPbI3) and (CH(NH2)2)PbI3 (FAPbI3) based perovskite solar cells (PSCs), respectively. Our finding provides a distinctive understanding on the roles of AMCs on the perovskite surface for PSCs.

Automated summary

Benzylammonium cation (BA) and difluorinated BA (DFBA) play different roles on the perovskite surface. BA transforms 3D perovskite into 2D perovskite, but the random orientation of 2D perovskite hinders charge extraction and increases nonradiative charge recombination. On the other hand, DFBA cannot form 2D perovskite, but it interacts directly with the perovskite surface, improving the contact with the Spiro-OMeTAD layer and promoting interfacial charge extraction, thus enhancing the efficiency of perovskite solar cells.