Lowering the dielectric mismatch for efficient inverted perovskite solar cells through incorporating cyano-functionalized fullerene additive

Fullerene derivatives especially [1,1]-phenyl-C61-butyric-acid-methyl-ester (PC61BM) have been commonly used as electron transport layers and additives of inverted (p-i-n) perovskite solar cells (PVKSCs); however the dielectric constant (the εr) PC61BM (3.8) is much smaller than those organolead halide hybrid perovskites (6.5 for CH3NH3PbI3 [MAPbI3]), resulting in unfavorable exciton dissociation impeded interfacial charge consequently undesirable nonradiative recombination. Herein, a novel cyanofunctionalized fullerene which two cyano groups are incorporated via rhodanine moiety (abbreviated C60-Rhd-CN) was synthesized introduced into MAPbI3 active layer to construct PVKSCs an anti-solvent method. The involvement electron-withdrawing within C60-Rhd-CN obviously increases εr value (5.1) relative (3.8), hence lowering mismatch between fullerene. Besides, enable strong coordination interactions with Pb2+ ions MAP-bI3, rendering efficient defect passivation perovskite. As result, incorporation facilitates suppresses recombination, affording dramatic power conversion efficiency (PCE) enhancement PVKSC devices from 18.43% 20.81%. Furthermore, helps improve ambient thermal stabilities devices. To elucidate critical role increasing enhancement, another analogous rhodanine-functionalized substituted by sulfur atom C60-Rhd-S) also synthesized, delivered lower PCE 19.45% C60-Rhd-CN-incorporated due mainly its (4.0).