Cyclopentadithiophene-benzothiadiazole oligomers and polymers; synthesis, characterisation, field-effect transistor and photovoltaic characteristics

Masaki Horie; Jeff Kettle; Chin-Yang Yu; Leszek A. Majewski; Shu-Wei Chang; James Kirkpatrick; Sachetan M. Tuladhar; Jenny Nelson; Brian R. Saunders; Michael L. Turner

doi:10.1039/C1JM12449H

Cyclopentadithiophene-benzothiadiazole oligomers and polymers; synthesis, characterisation, field-effect transistor and photovoltaic characteristics†

Masaki Horie,*^ac Jeff Kettle,^bc Chin-Yang Yu,^dc Leszek A. Majewski,^e Shu-Wei Chang,^a James Kirkpatrick,^f Sachetan M. Tuladhar,^g Jenny Nelson,^g Brian R. Saunders^h and Michael L. Turner*^c

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* Corresponding authors

^a Frontier Research Center on Fundamental and Applied Sciences of Matters, Department of Chemical Engineering, National Tsing-Hua University, 101, Sec. 2, Kuang-Fu Road, Hsin-Chu, Taiwan
E-mail: mhorie@mx.nthu.edu.tw

^b School of Electronic Engineering, Bangor University, Dean st., Bangor, Gwynedd, Wales, UK

^c Organic Materials Innovation Centre, School of Chemistry, University of Manchester, Oxford Road, Manchester, UK
E-mail: michael.turner@manchester.ac.uk

^d Department of Materials Science and Engineering, National Taiwan University of Science and Technology, 43, Section 4, Keelung Road, Taipei, Taiwan

^e School of Electrical and Electronic Engineering, University of Manchester, Manchester, UK

^f Oxford Martin School, University of Oxford, UK

^g Department of Physics, Imperial College London, London, UK

^h School of Materials, University of Manchester, Grosvenor St, Manchester, UK

Abstract

Conjugated oligomers with various ratios of cyclopentadithiophene (CPDT) to benzothiadiazole (BT) repeating units are reported. These oligomers can be polymerised to high molecular weight polymers (M_n > 100k) by oxidative polymerisation using iron(III)chloride. The electronic properties of these materials were examined by cyclic voltammetry and UV-vis spectroscopy and the results compared to those calculated using density functional theory (DFT). Polymers with optimum ratios of CPDT : BT (2 : 1) units show hole mobilities in excess of 10⁻² cm² V⁻¹ s⁻¹ as the active layer in organic field effect transistors (OFETs). Bulk heterojunction organic photovoltaic (OPV) devices of these polymers with PCBM as the electron acceptor show a power conversion efficiency of 2.1% when processed in the absence of any additives. The reported OFET performance is significantly higher than the parent PCPDTBT alternating copolymer (CPDT : BT = 1 : 1) and also shows a moderate improvement in OPV performance.

Journal of Materials Chemistry

Cyclopentadithiophene-benzothiadiazole oligomers and polymers; synthesis, characterisation, field-effect transistor and photovoltaic characteristics†

Abstract

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