Synthesis, characterization and optoelectronic properties of a new perylene diimide–benzimidazole type solar light harvesting dye

• Benzimidazole-substituted PDI dye for solution-processed BHJC was synthesized.
• Aggregation tendency of dye in the presence of P3HT polymer was observed.
• Electron mobility of PDI dye is calculated to be higher than the hole mobility.

A perylene diimide type small molecule (BI-PDI) has been synthesized through Suzuki coupling reaction between N,N′-bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-tetracarboxylic diimide and 2-(2-hydroxyphenyl)-7-phenyl-1H-benzimidazole-4-boronic acid. BI-PDI small molecule has showed an absorption band between 350 and 750 nm on thin films. HOMO and LUMO energy levels of BI-PDI dye have been calculated to be about −5.92 eV and −3.82 eV, respectively. Solution-processed bulk heterojunction (BHJ) solar cells have been constructed using BI-PDI as donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as acceptor or poly(3-hexylthiophene) (P3HT) as donor and BI-PDI as acceptor. The external quantum efficiencies (EQE) of the devices cover the most of the visible region between 400 and 700 nm for both configurations. Photovoltaic performances of BI-PDI-based organic solar cells are limited by the aggregation tendency of PDI structure and poor hole/electron mobilities of the active layer.

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