Block Copolymer-Tuned Fullerene Electron Transport Layer Enhances the Efficiency of Perovskite Photovoltaics

Abstract

In this study, we enhanced the power conversion efficiency (PCE) of perovskite solar cells by employing an electron transfer layer (ETL) comprising [6,6]phenyl-C-61-butyric acid methyl ester (PC61BM) and, to optimize its morphology, a small amount of the block copolymer polystyreneb-poly(ethylene oxide) (PS-b-PEO), positioned on the perovskite active layer. When incorporating 0.373 wt, % PS-b-PEO into PC61BM, the PCE of the perovskite photovoltaic device increased from- 9.4% to 13.4%, a relative increase of 43%, because of a large enhancement in the fill factor of the device. To\' decipher the intricate morphology of the ETL, we used synchrdtron grazing-incidence small-angle X-ray scattering for determining the PC61BM cluster site, atomic force microscopy and scanning electron microscopy for probing the-surface, and transmission electron microscopy for observing the aggregation of PC61BM in the ETL. We found that the interaction between PS-b-PEO and PC61BM resulted in smaller PC61BM dusters that further aggregated into dendritic structures in some domains, a result of the similar polarities of the PS block and PC61BM; this behavior could \'be used to tune the morphology of the ETL. The optimal PS-b-PEO-mediated PC61BM cluster size in the ETT, was 17 nm, a large reduction from 59 nin for the pristine PC61BM layer. This approach ofincorporating a small amount of nanostructured block copolymer into a fullerene allowed us to effectively tune the morphology of the ETL on the perovskite active layer and resulted in enhanced fill factors of the devices and thus their device efficiency.