Synthesis, characterization and photovoltaic performance of novel glass-forming perylenediimide derivatives

Abstract

Novel glass-forming perylene-3,4,9,10-tetracarboxylic diimide (PDI) derivatives were synthesized from 1,7-dibromoperylene-3,4,9,10-tetracarboxylic diimides by nucleophilic substitution with a glass-forming mexylaminotriazine unit, characterized, and their performance as electron acceptors in bulk heterojunction photovoltaic cells with P3HT as donor were studied. Imide groups (octyl and 2,6-diisopropylphenyl) and bay substituents (bromo or pyrrolidinyl) were used to study the impact of sterics and electronics on device performance. The HOMO and LUMO levels of the materials were determined using cyclic voltammetry. The morphology and packing behavior of molecules in films of blends with P3HT were studied using Atomic Force Microscopy and X-ray diffraction, and in all four cases, the PDI derivatives remain in the amorphous phase, while the P3HT portion of the blends crystallizes. The devices gave photovoltaic performances ranging from 0.2 to 0.6%, and while the bay substituents showed negligible impact on device performance, switching from bulky 2,6-diisopropylphenyl imide groups to linear octyl chains improved the efficiency of the devices by 36%, current density by 66% and fill factor by 16%. The performances observed for devices incorporating these PDI glasses are comparable to that of devices with crystalline PDI acceptors.