Asymmetric perylene-diimide-based polymeric acceptor integrating alkoxy and alkyl side chains: Synthesis and application for all-polymer solar cell

Alkoxy side chain embodying the large electronegative oxygen played the critical role in tuning the optoelec-tronic and photovoltaic properties. However, few efforts devoted to incorporating the alkoxy side chain into perylene diimide (PDI) building block. In this contribution, one PDI-containing asymmetric polymeric acceptor PPDI-HD-OHD-T bearing 2-hexyldecyl (HD) and 2-hexyldecyloxy (OHD) side chains was developed. Also, two symmetric polymeric acceptors PPDI-HD2-T and PPDI-OHD2-T with identical HD and OHD side chains were prepared to systematically study the impact of bonding OHD side chain on light-harvesting and electrochemical property, molecular configuration, solar cell performance and morphology. Moving from alkyl to alkoxy chains resulted in at first a red-shifted and then a blue-shifted absorption maximum, gradually downshifted HOMO and LUMO energy levels, better molecular planarity, enhanced solution and film state aggregation, and improved photo-stability, these changes resulted from the N-O sigma-inductive effect induced by the inserted oxygen, along with the increased number of alkoxy side chain of PDI ring. Furthermore, PPDI-HD-OHD-T acquired a more complementary absorption to PTB7-Th, increased electron mobility and benefited morphology. Thereupon, both improved JSC and FF in PPDI-HD-OHD-T-based device contributed to the boosted PCE of 2.08%, which was higher than those of symmetric side chains PPDI-HD2-T and PPDI-HD-OHD-T-based devices. To our knowledge, it is the first attempt to introduce the alkoxy side chain to N-position of PDI to construct asymmetric polymer acceptor and demonstrated that skillfully tuning the side-chain can effectively affect the electron distribution, molecular configuration, aggregation, charge mobility, and achieve improved device efficiency in all-polymer solar cell.