Naphthodithieno[3,2-b]thiophene-based donor-acceptor copolymers: Synthesis, characterization, and their photovoltaic and charge transport properties

• Dialkoxyl-substituted naphthodithieno [3,2-b]thiophene (NDTT)-based copolymers were synthetized and characterized.
• Polymer field-effect transistors were fabricated and a high mobility up to 0.07 cm2 V−1 s−1 was obtained.
• Polymer solar cells were fabricated and a power conversion efficiency of 3.54% was obtained.

Herein, we report the synthesis, characterization, and their photovoltaic and field–effect properties of two dialkoxyl-substituted naphthodithieno[3,2-b]thiophene (NDTT)-based copolymers, namely P1 and P2. The NDTT-based copolymers exhibit broad absorption profiles throughout the visible spectrum up to ca. 800 nm. The copolymers have HOMO/LUMO energy levels of ca. –5.14 eV/–3.52 eV. The dialkoxyl-substituted NDTT units endow the copolymers with enhanced solution processability, and crystalline stacking thin films with small π–π distances of down to 3.59 Å. Polymer-fullerene bulk heterojunction solar cells that fabricated from a blend of P2/PC71BM using diiodooctane as a solvent additive, afforded the highest power conversion efficiency of 3.54%. Solution-processed polymer field-effect transistors based on P1 with bottom-gate bottom-contact geometry exhibited promising hole mobilities of 0.070 cm2 V−1 s−1.

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