Synthesis and characterization of porphyrin-terthiophene and oligothiophene π-conjugated copolymers for polymer solar cells

Two novel conjugated polymers with alternating main chain structures of zinc porphyrin-terthiophene (P-PTT) and zinc porphyrin-oligothiophene (P-POT) were synthesized by Stille reaction. The effect of different lengths of thiophene chains on the thermal, optical, electrochemical, and photovoltaic properties of the two copolymers were investigated in detail. P-PTT exhibited higher onset decomposition temperature (392 °C) and glass-transition temperature (152 °C) than those of P-POT. The introduction of thiophene units in the meso-aryl positions of porphyrin resulted in the red shift and broader absorption spectrum compared with zinc porphyrin (PZn) monomer both in chloroform solutions and on thin solid films. The electrochemical properties indicated that the energy levels of the polymers were suitable for efficient charge transfer and separation at the interface between the polymer donor and PCBM acceptor. The bulk heterojunction solar cells based on P-PTT and P-POT showed power conversion efficiencies up to 0.32% and 0.18%, respectively.