One, two and three-branched triphenylamine–oligothiophene hybrids for solution-processed solar cells

A series of one, two and three-branched push–pull molecules (TPA-1T-CA, TPA-2T-CA, TPA-3T-CA, L(TPA-3T-CA) and S(TPA-3T-CA)) with triphenylamine–oligothiophene hybrids as donor groups and alkyl cyanoacetate as acceptor end groups were synthesized and investigated as electron donors in solution-processed organic solar cells (OSCs). These push–pull molecules showed excellent thermal stability with decomposition temperatures over 330 °C, strong optical absorption at 300–700 nm, deep HOMO energy levels (−5.2 to −5.5 eV), and relatively high hole mobilities (4 × 10−4 to 8 × 10−3 cm2 V−1 s−1). OSCs based on blends of these donors and PC71BM acceptors exhibited power conversion efficiencies of 3.2% to 4%. The effects of oligothiophene bridge length and branch number on absorption, energy level, charge transport, morphology and photovoltaic properties of the molecules were investigated.