Highly efficient single-layer blue polymer light-emitting diodes based on hole-transporting group substituted poly(fluorene-co-dibenzothiophene-S,S-dioxide)

We developed a series of high-performance blue light-emitting polymers that contain hole-transport moieties comprising carbazole or triphenylamine substituents in the side chains of random copolymer poly(fluorene-co-dibenzothiophene-S, S-dioxide) (PFSO). The incorporation of these hole-transport species had negligible effects on the optical properties of the polymers but obviously facilitated hole injection from the anode, leading to significant improvements in hole/electron flux in the emissive layer. Interestingly, the copolymers that comprised either carbazole or triphenylamine substituents exhibited dramatically enhanced luminous efficiencies compared with the original copolymer. A PFSO-T5-based device yielded an excellent luminous efficiency of 7.04 cd A(-1) at a brightness of 1000 cd m(-2) with CIE coordinates of (0.16, 0.18), the highest efficiency reported so far for blue light-emitting polymers based on single-layer devices. The electroluminescent spectra of the PFSO-T5-based device exhibited excellent stability, as evidenced by a lack of change as the driving voltage increased from 4 to 8 V. These results indicate that the introduction of a hole-transporting group in the side chain is a very promising strategy for the development of highly efficient blue polymers for single-layer devices.