The photovoltaic behaviors of PPV- and PPE-type conjugated polymers featured with diketopyrrolopyrrole (DPP) units

The photovoltaic behaviors of diketopyrrolopyrrole (DPP) embedded poly(phenylenevinylene) (C8-DPP-PPV) and poly(phenyleneethynylene) (C10-DPP-PPE) were investigated. The two polymers exhibited good solubility in common organic solvents, high thermal stability and broad UV/visible absorption ranging from 300 to 600 nm in films. Their optical band gaps were found to be 1.94 eV for C8-DPP-PPV and 2.05 eV for C10-DPP-PPE. Moreover, their HOMO energy levels were relatively low at around −5.6 to −5.8 eV as estimated by electrochemical measurements. The polymer/PCBM bulk heterojunction solar cells exhibited a power conversion efficiency of 0.16% for C10-DPP-PPE. In addition, all-polymer solar cells consisting of C10-DPP-PPE/P3HT were also fabricated in view of the potential of C10-DPP-PPE as a polymeric acceptor, revealing an efficiency of 0.01%.