Design,Synthesis,Characterization And Photovoltaic Properties Of Diindenocarbazole-Based Copolymers

Carbazole and its derivatives are a type of nitrogen-containing aromatic heterocylic building blocks, which have a rigid and planar structure with extended ?-conjugated system. When used for the synthesis of copolymers, materials with excellent photo and thermal stability as well as high charge transport mobility can be obtained. In this thesis, a series of large bandgap conjugated polymers based on diindenocarbazole ?DIC? and dithienylbenzothiadiazole ?DTBT? alternating building blocks have been designed and prepared to investigate the effects of side chains on their photovoltaic performance. All the polymers are soluble in common organic solvents and show similar optical bandgaps of 2.0 eV as well as deep-lying Highest Occupied Molecular Orbital ?HOMO? energy levels ?below -5.47 eV?. Bulk heterojunction ?BHJ? polymer solar cells ?PSCs? with phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the electron-accepting material were fabricated. The side chains on the polymer backbone have a strong impact on the film morphology of polymer:PC₇₁BM blends. A large-domain-size phase separation was found for the polymers with long side chains, while those with relatively short alkyl chains could form uniform films featuring relatively small-domain-size phase separation. The polymer with a methyl group on the nitrogen atom of DIC unit displays a relatively high hole mobility up to 5.8×10^-4 cm²v^-1s^-1. In the end, PSCs based on PC1BT6.PC₇₁BM exhibit an outstanding power conversion efficiency ?PCE? up to 7.34% with a high open-circuit voltage of 0.95 V. Our results demonstrate that the judicious design of side chains is effective in improving photovoltaic performance of the diindenocarbazole-based polymers. Besides, we also designed and synthesized a polymer ?P1? based on DIC and dithiophenylbenzothiadiazole ?DTTBT?. BHJ PSCs with PC₇₁BM were fabricated to investigate the photovoltaic properties. Without extensive optimization, a PCE of 6.7% was obtained for the PSCs based on P1:PC₇₁BM ?1:4, wt%? with DIO ?0.5%, v/v?.