Evolved structure of thiazolothiazole based small molecules towards enhanced efficiency in organic solar cells

Small molecule donors T0-T2 with thiazolothiazole as acceptor unit, triphenylamine as donor unit and thiophene with different number as bridge are synthesized. With increasing thiophene number and conjugation length, these molecules exhibit red-shifted absorption (300-600 nm), slightly up-shifted HOMO levels (-5.31 to -5.28 eV), slightly down-shifted LUMO levels (-2.64 to -2.75 eV), and reduced optical band gaps (2.55-2.11 eV). Solution processed organic solar cells based on T0-T2/PC71BM (1:4, w/w) after thermal annealing exhibit power conversion efficiency up to 2.19%, 3.73% and 4.05% under AM 1.5G illumination (100 mW/cm(2)), respectively. Effects of thermal annealing on morphology, charge transport and photovoltaic property of blend films are investigated. (C) 2012 Elsevier B.V. All rights reserved.