Synthesis, characterization and comparative photovoltaic behavior of diketopyrrolopyrrole (DPP)-containing poly(phenylene vinylene)s varying at N-alkyl or 3,6-aryl substituents in DPP units

Three new diketopyrrolopyrrole (DPP)-containing poly(phenylene vinylene)s varying at N-alkyl or 3,6-aryl substituents in DPP units, abbreviated as C6DPPDHPV, C6DTDPPDHPV, and C62DTDPPDHPV, were designed to comparatively study the structural effects on their photophysical, electrochemical properties, molecular organization and photovoltaic properties. The polymers exhibited remarkably broad UV–vis absorption spectra covering a major part of the wavelength range of visible light in the solar spectrum, and small bandgaps between 1.4 and 1.9 eV. X-ray diffraction and cyclic voltammetry measurements revealed that N-alkyl and 3,6-aryl in DPP unit played a key role in tuning their molecular organization as well as electrochemical behavior. The bulk heterojunction photovoltaic devices employing the three polymers as electron donors, together with PC61BM as electron acceptor, were examined. C6DPPDHPV based device showed the highest energy conversion efficiency of 0.72%. Lower hole mobilities and relatively higher HOMO energy levels may be responsible for inferior performance of C6DTDPPDHPV and C62DTDPPDHPV-based devices. Moreover, the C6DPPDHPV was preliminarily evaluated as active material in organic thin film transistor.