New donor–acceptor-type copolymers containing dioxocycloalkene-annelated thiophenes as electron-accepting units have been designed and synthesized for application to p-type organic semiconducting materials in organic photovoltaics. The investigation of their photophysical and electrochemical properties revealed that these copolymers possessed low optical bandgaps (from 1.63 to 1.92 eV) and low-lying HOMO energy levels (from −5.41 to −5.33 eV). Organic field-effect transistor measurements revealed that these copolymers had hole-transporting characteristics with mobilities on the order of 10–7–10–4 cm2 V–1 s–1. The bulk-heterojunction photovoltaic devices fabricated from blends of these copolymers with fullerene derivatives as acceptors showed high power conversion efficiencies of up to 4.87%, with an open-circuit voltage of 0.90 V, a short-circuit current of 11.46 mA cm–2, and a fill factor of 0.48 under air mass 1.5 simulated solar illumination.

A systematic study on the design of fulleropyrrolidine derivatives as the acceptor of photovoltaic cells has been carried out using poly(3-hexylthiophene) (P3HT) as the model base polymer. It was found that N-methoxyethoxyethyl-2-(2-methoxyphenyl)fulleropyrrolidine worked as a good acceptor partner with P3HT and a high power conversion efficiency (PCE) (3.44%) was obtained; this is superior to that of the P3HT polymer including methyl [6,6]-phenyl-C61-butylate ([C60]-PCBM) under the same experimental conditions.

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