Synthesis and characterization of poly(dialkylterthiophene-bithiophene) and poly(dialkylterthiophene-thienothiophene) for organic thin film transistors and organic photovoltaic cells

• New copolymers based dialkylterthiophene.
• Among copolymers, PBTOT had relatively good solubility and crystalline structure.
• PBTOT showed field effect mobility of 1.73 × 10−2 cm2 V−1 S−1.
• PBTOT showed power conversion efficiency of 3.2%.

We designed new polymers composed of dialkylated terthiophene and thieno[3,2-b]thiophene, 2,2′-bithiophene for the fabrication of organic thin film transistors and polymer solar cells. Poly[5-(thieno[3,2-b]thiophene-2-yl)3′,4′-dioctyl-2,2′:5′,2″-terthiophene] (PTTOT), and poly[5-((2,2′-bithiophene)-5-yl)3′,4′-dioctyl-2,2′:5′,2″-terthiophene] (PBTOT) were synthesized via Stille coupling and Suzuki coupling reaction. The obtained polymers were confirmed by 1H NMR and FT-IR spectra. The weight average molecular, the thermal, optical and electronic properties of the polymers were investigated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), ultraviolet–visible (UV–vis) absorption and photoluminescence (PL) spectroscopies and cyclic voltammetry (CV). The crystallinity of polymer films was investigated by X-ray diffraction (XRD). Field-effect hole mobilities of PTTOT and PBTOT based solution-processed OTFTs were 3.54 × 10−3 cm2 V−1 S−1 and 1.73 × 10−2 cm2 V−1 S−1, respectively. And, each of the polymers was investigated as an electron donor material with PC71BM as an electron acceptor in bulk hetero junction solar cells. The polymers of PTTOT and PBTOT showed the power conversion efficiency (PCE) of 0.096% (Jsc = 0.1 mA/cm−2, FF = 83.49%) and 3.2% (JSC = 8.9 mA/cm−2, FF = 51.9%), respectively.

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