A new strategy for fabricating organic photovoltaic devices with stable D/A double-channel network to enhance performance using self-assembling all-conjugated diblock copolymer

Abstract

In this study, we demonstrate the cooperative self-assembly of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and an all-conjugated poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene) (PPP-P3HT) block copolymer to yield organic photovoltaic devices with enhanced solar cell performance and long-term stability. By a combination of TEM, GISAXS and GIWAXS structural investigations, it was found that a PPP-P3HT/PCBM hybrid film adopts a donor/acceptor (D/A) double-channel network (DCN) structure via simple spin-coating by self-organizing highly ordered and long-ranged crystalline P3HT nanofibrils as a hole-transporting channel, and the surrounding amorphous PPP domain with PCBM confined and dispersed within as the other electron-transporting channel. As a consequence of the structural development, the block copolymer hybrid solar cells could afford significant improvements in the charge transporting property and enhanced exciton separation, leading to a substantial improvement in the power conversion efficiency (PCE) of the resulting device. The photovoltaic devices with the DCN structure gave a high average PCE of 3.43% as compared to only 2.77% from a conventional P3HT/PCBM bulk heterojuction (BHJ) solar cell. Notably, the DCN solar cell showed significant improvements in thermal stability over the P3HT/PCBM BHJ solar cell in accelerated testing experiments. This enhancement is believed to be due to the nanoconfinement effect of the double-channel structure on the PCBM molecules, thereby averting PCBM aggregation problems typically occurring in BHJ devices. These results show promise for the practical usage of all-conjugated block copolymers with different main chain moieties towards the fabrication of organic photovoltaic devices with superior stability and competitive optoelectronic properties.