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 degrees C, strong optical absorption at 300-700 nm, deep HOMO energy levels (-5.2 to -5.5 eV), and relatively high hole mobilities (4 x 10(-4) to 8 x 10(-3) cm(2) 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.