Synthesis and Photovoltaic Properties of 1,8-Carbazole-Based Donor-Acceptor Type Conjugated Polymers

1,8-Diethynylcarbazole-based conjugated polymers were synthesized by the acetylenic oxidative coupling reaction or Pd-catalyzed Sonogashira reaction of the newly designed 3,6-dialkylated 1,8-diethynylcarbazole monomers. In particular, the Sonogashira polycondensation was effective for the preparation of donoracceptor type alternating copolymers. The UV-vis absorption and fluorescence spectra of the polymers revealed the strength of the donoracceptor interactions as well as their self-assembling features. The combination of electrochemical redox potentials and optical band gaps enabled the estimation of the polymer energy levels. The bulk-heterojunction solar cells composed of these promising polymers and PCBM exhibited a photoconversion efficiency (PCE) of 0.24%. It was determined that the partial doping of the bulk-heterojunction layer increased the open-circuit voltage (Voc), but decreased the short-circuit current (Jsc).