| Abstract | Novel p-type and low bandgap penta- and hexa-thiophenes asymmetrically endcapped with solubilizing triarylamine or triarylamino-substituted carbazole dendron and dicyanovinyl groups, namely, PhNOF-OT(n)-DCN and G2-OT(n)-DCN, respectively where n ¼ 5–6 for solution-processable photovoltaic applications have been synthesized and investigated. With the incorporation of a solubilizing electron-donating group, the highly extended oligothiophenes are highly soluble in common organic solvents and solution-processable. Upon extending the oligothiophene backbone, there is a strong increase in the absorption around 420 nm in addition to the intramolecular charge-transfer absorption (520 nm) which results in a strong spectral broadening. The optical band-gap of these donor–acceptor oligothiophene thin-films greatly reduces to 1.85 eV. The solution-processed bulk heterojunction PV cells fabricated from these materials blended with PCBM as an acceptor showed a PCE up to 1.72% with Voc ¼ 0.79 V in an as-fabricated device. Our findings also suggest that highly extended donor–acceptor oligomers can be useful for a p-type, low-bandgap semiconductor for solution-processable bulk heterojunction PV cells. |
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