Impact of fullerene derivative isomeric purity on the performance of inverted planar perovskite solar cells

The effect of utilizing a pure cis-alpha-dimethoxy carbonyl fulleropyrrolidine C-70 (DMEC70) isomer as the electron transporting material (ETM) in inverted perovskite solar cells (PSCs) was evaluated. The asprepared C-70 mono-adduct products are mixtures of regioisomers and the interest was to evaluate them independently as ETMs. Three different cis-DMEC70 isomers (alpha, beta-endo and beta-exo) (mix-DMEC70) were synthesized and purified by HPLC. It was found that PSCs based on the pure alpha-DMEC70 exhibit a substantially enhanced maximum power conversion efficiency (PCE) of 18.6% as compared to devices based on the mixed-DMEC70 isomers that yielded a PCE of 16.4%. A maximum PCE of 15.7% was observed for devices based on [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). This work points out the importance of using pure fullerene derivative isomers as ETMs to reduce the intrinsic energy disorder, which enhances the overall device performance.