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

Abstract

The effect of utilizing a pure <i>cis</i>-α-dimethoxy carbonyl fulleropyrrolidine C₇₀ (DMEC₇₀) isomer as the electron transporting material (ETM) in inverted perovskite solar cells (PSCs) was evaluated. The as-prepared C₇₀ mono-adduct products are mixtures of regioisomers and the interest was to evaluate them independently as ETMs. Three different <i>cis</i>-DMEC₇₀ isomers (α, β-<i>endo</i> and β-<i>exo</i>) (mix-DMEC₇₀) were synthesized and purified by HPLC. It was found that PSCs based on the pure <b>α-DMEC₇₀</b> 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.