Molecular base and interfacial enrichment of chain entangle in amorphous conjugated polymers: Role of racemic alkyl side groups

Abstract

Abstract Clear structure characterization is the basics of performance analysis, which is difficult for the complex structure of amorphous conjugated polymers. In this work, we have given solid evidence in copolymer of fluorene and carbazole that the carbazole with racemic branched alkyl side chain tend to form chain entanglement in high concentration of solution and thin film. The single crystal structure of two racemic carbazole dimer with stronger π-π interaction, which 1HNMR peaks is well corresponding to that of racemic polymer at high concentration and proves the existence of chain entanglement in racemic polymer. The chain entanglement segment with high molecular weight and low energy level (estimated as about 3% and absent in the chiral polymer) have enriched at the interface during film fabrication, which induce strong charge trapping and excited state quenching during the working of optoelectronic devices. These chain entanglement would be well restrained by chiral substitution, which induce one order of magnitudes improvement of device brightness and efficiency. These results indicate that the chain entangle at interface and charge trapping play the key role of bad device performance, which help to explore the instability origin and performance promotion.