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

Abstract

Alkoxy side chain embodying the large electronegative oxygen played the critical role in tuning the optoelectronic 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 σ-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.