Cyclopentadithiophene–naphthalenediimide polymers; synthesis, characterisation, and n-type semiconducting properties in field-effect transistors and photovoltaic devices

• Cyclopentadithiophene–naphthalenediimide oligomers were prepared by direct arylation.
• The oligomers were polymerised by oxidative reaction using iron(III)chloride.
• The polymer films show deep-red absorption up to 1100 nm with a bandgap of 1.1 eV.
• The polymers exhibit only n-type semiconducting properties in OFETs and OPVs.

The synthesis, characterisation, and device performance of a series of cyclopentadithiophene (CPDT)-naphthalenediimide (NDI) donor-acceptor-donor (D-A-D) polymers is reported. The monomers with various alkyl chains are synthesised via direct arylation using palladium complex catalyst. The monomers are then polymerised by oxidative polymerisation using FeCl3 to provide high molecular weight polymers (Mn = 21,800–76,000). The polymer films show deep-red absorption including near-infrared region up to 1100 nm to give optical bandgap of approximately 1.16 eV. The polymers exhibit only n-type semiconducting properties giving the highest electron mobility of 9 × 10-3 cm2 V−1 s−1 in organic field-effect transistors (OFETs). Organic photovoltaic (OPV) devices are fabricated from solutions of the polymers as acceptors and poly(3-hexylthiophene) (P3HT) as a donor.

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