Synthesis, characterization and photovoltaic properties of new iridium-containing conjugated polymers

Abstract

Novel donor-acceptor (D-A) copolymers P1-P5 with iridium-complexed moieties in their side chains have been synthesized on the base of new iridium-containing monomer. These copolymers absorb visible light in broad spectral range up to 680 nm. Optical bandgaps of P1-P5 are in the range of 1.96 - 2.08 eV, respectively. HOMO and LUMO energy levels of the polymers P1-P5 were estimated from cyclic voltanunetry measurement indicates that these copolymers are suitable for electron donor along PC71BM as electron acceptor for the hulk heterojunction polymer solar cells. BHJ polymer solar cells were developed based on blend compositions (Pl-P5):PC7IBM. The values of Jsc, Voc, and FP are in the ranges of 0.95-4.44 mAfcm2; 0.67-0.69 V and 34.6-56.8%, power conversion efficiencies (PCE) are in the range of 0.22-1.74%, respectively, highest 1.74 for P3. Increasing of the photovoltaic parameters was achieved with increasing of iridium complexes percentage in the polymers due to involvement of triplet effects. The improvement in the efficiency of the triplet-forming polymers P2 and P3 in comparison with P1 appears to be due to the formation of triplet excitons in comparison with singlet excitons in the polymer P1 that does not contain heavy metals. With further increase in the content of iridium complex fragments in polymers, for example up to 3 mol% for polymer P4, the efficiency falls to 1.23% and further decreased up to 0.22 % for P5.