Elucidating roles of fulleropyrrolidine-based materials as extraordinary electron transporters for boosting efficiency of perovskite photovoltaics

Abstract

To achieve an ideal electron transfer layer (ETL) for perovskite solar cell (PSC), effective compounds were developed based on fullerene C60 functionalized with a pyrrolidine ring (fulleropyrrolidine), to which a cyanoethyl group, a thiophene ring, and four DNA bases were attached. Density functional theory (DFT) calculations were employed to study structural, electronic, optical, and electron mobility features of these materials. To more precisely determine the HOMO and LUMO energy levels of all samples, the NBO calculations were accomplished at PBE0-D3/6-31G(d,p) theoretical level. The LUMO levels of all ETL samples could be aligned with the conduction band of perovskite CsFAMAPbIBr via their coupling within fabricated PSCs, enabling easy electron injection from CsFAMAPbIBr to the Ag electrode. All functionalized fullerene C60–based ETLs exhibited very high electron mobilities in the range of 0.744–1.598 cm2V−1s−1 which were significantly greater than 1.461 × 10−5 cm2V−1s−1 for pure C60 as the reference. High fill factors (FFs), power conversion efficiencies (PCEs), and open circuit voltages (VOC) were measured for PSC devices with C60–based ETLs, varying within the ranges of 0.892–0.897, 22.489–23.984 %, and 1.111–1.179 V, respectively, indicating they could yield excellent photovoltaic parameters.