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

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% (J _sc = 0.1 mA/cm^-2, FF = 83.49%) and 3.2% (J_SC = 8.9 mA/cm^-2, FF = 51.9%), respectively.