Benzodithiophenedione and diketopyrrolopyrrole based conjugated copolymers for organic thin-film transistors by structure modulation

• Three polymers based on BDD unit were synthesized and characterization.
• This is the first investigation on the OTFTs of BDD-based polymers.
• The OTFT performances were optimized by tailoring structure and annealing.
• The optimized P3 exhibited balanced hole and electron transport.
• The phototransistors showed a high photocurrent/dark-current ratio of 6.4 × 103.

Three copolymers (P1, P2, and P3) based on benzodithiophenedione and diketopyrrolopyrrole units were synthesized by Suzuki reaction. The thermal, optical, electrochemical, microstructure, charge transport and phototransistor properties of the copolymers were also investigated. The field-effect performances of the copolymers were optimized by tailoring their structure and using thermal annealing. The three copolymers exhibited ambipolar transport under vacuum, but hole characteristics in air. The optimized copolymer P3 exhibited a balanced hole and electron mobility of 0.022 and 0.028 cm2 V−1 s−1, respectively, under vacuum conditions, but hole transport in air with a hole mobility of as high as 0.034 cm2 V−1 s−1. Phototransistors based on P3 showed a photocurrent/dark current ratio of 6.4 × 103 under near-infrared light illumination (808 nm). This is the first investigation on the field-effect and phototransistor performances of benzodithiophenedione-based copolymers.

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