Synthesis and characterization of cyclic P3HT as a donor polymer for organic solar cells

• Published in: Journal of polymer science. Part B, Polymer physics Polymer physics, 2019-03, Vol.57 (5), p.266-271
• Main Authors: Fukushima, Tatsuya, Ishibashi, Hirotaka, Suemasa, Daichi, Nakamura, Ryosuke, Yomogida, Masanobu, Isono, Takuya, Satoh, Toshifumi, Kaji, Hironori
• Format: Article
• Language: English
• Subjects: Butyric acid; carrier mobility; Chemical synthesis; cyclic polythiophene; Dispersion; electron collection; Electron transport; Energy conversion efficiency; Hole mobility; Organic chemistry; organic solar cell; Photoelectric effect; Photoelectric emission; Photoelectricity; Photovoltaic cells; Solar cells; time‐of‐flight method
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.24779

ABSTRACT In this study, cyclic poly(3‐hexylthiophene‐2,5‐diyl) (c‐P3HT) with a controlled Mn was synthesized by the intramolecular cyclization of α‐bromo‐ω‐ethynyl‐functionalized P3HT via the Sonogashira coupling reaction. The effect of the cyclic structure, which does not have terminal groups of polymers, on the photoelectric conversion characteristics was investigated in comparison to linear P3HT (l‐P3HT). c‐P3HT was successfully synthesized with Mn ≈ 17,000, dispersity ≈ 1.2, and regioregularity ≈ 99%. The hole mobility was determined to be 5.1 × 10−4 cm2 V−1 s−1 by time‐of‐flight (TOF) experiment. This was comparable to that of l‐P3HT of 5.6 × 10−4 cm2 V−1 s−1. Organic solar cell systems were fabricated with each polymer by blending them with [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM). The l‐P3HT:PC71BM system showed a dispersive TOF photocurrent profile for electron transport, whereas a nondispersive profile was observed for c‐P3HT:PC71BM. In addition, an amount of collected electrons in c‐P3HT:PC71BM was greater than that in l‐P3HT:PC71BM for TOF experiments. The photoelectric conversion characteristics were improved by using c‐P3HT rather than l‐P3HT (power conversion efficiency [PCE] = 4.05% vs 3.23%), reflecting the nondispersive transport and the improvement of electron collection. PCEs will be much improved by applying this cyclic concept to highly‐efficient OSC polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 266–271 π‐conjugated cyclic molecules are of interest in molecular engineering and are attractive features for use in organic electronics. Polymer‐based organic solar cells are fabricated from synthesized cyclic poly(3‐hexylthiophene‐2,5‐diyl) and a typical fullerene derivative as donor and acceptor materials, respectively. The cyclic structure affects the electron transport properties of the acceptor in the blend film and improves the power conversion efficiency compared to linear P3HT (4.05% vs 3.23%).