Improved Performance and Stability of Inverted Planar Perovskite Solar Cells Using Fulleropyrrolidine Layers

Inverted planar structure perovskite solar cells (PSCs), due to their low-temperature precessing and lack of hysteretic problems, are attracting increased attention by researchers around the world. Fullerene derivatives are the most widely used electron transport materials (ETMs) in inverted planar perovskite solar cells, especially [6,6]-phenyl-C₆₁-butyric acid methylester (PC₆₁BM), which exhibits very good performance. However, to the best of our knowledge, the influence of adducts on fullerene-based PSCs performance has not been fully explored to date. In this work, two fullerene derivatives, 2,5-(dimethyl ester) C₆₀ fulleropyrrolidine (DMEC₆₀) and the analogous C₇₀ derivative (DMEC₇₀), were synthesized in high yield via a 1,3-dipolar cycloaddition reaction at room temperature and incorporated into CH₃NH₃PbI₃ perovskite solar cells as electron transport materials. Possibly because the attached pyrrolidine ester groups are able to coordinate with the perovskite layer, the devices based on DMEC₆₀ and DMEC₇₀ achieved power conversion efficiencies (PCE) of 15.2% and 16.4%, respectively. Not only were both devices' efficiencies higher than those based on PC₆₁BM and PC₇₁BM, but their stabilities were also higher than those for PCBM-based devices. The results suggest that DMEC₆₀ and DMEC₇₀ are better alternatives than PC₆₁BM and PC₇₁BM for the ETMs in PSCs.