Improving the Electroluminescent Performance of Blue Light-Emitting Polymers by Side-Chain Modification.

Abstract

Blue light-emitting polymers are in urgent demand for new-generation display and solid-state lighting devices fabricated through low-cost wet processing. However, their current performances are far from satisfactory. Here, we developed a series of poly(fluorene-co-dibenzothiophene-S,S-dioxides) (PFSOs) bearing different alkyl chains, alkoxyphenyl chains, or both alkylaryl and alkoxyphenyl side chains. The introduction of alkoxyphenyl groups moderately enhanced the electron-donating ability of the polymers, leading to more balanced charge carrier fluxes. Meanwhile, asymmetric bulky side chains enabled more pronounced variation of molecular conformation while restraining the intermolecular aggregation of polymers, resulting in a lower refractive index, thus facilitating light extraction compared with polymers based on the same two alkyl or alkoxyphenyl side chains. Polymer light-emitting devices based on PFSO-BMD with asymmetric side chains exhibited a maximum luminous efficiency of 8.58 cd A-1, associated with pure blue Commission Internationale de l'Eclairage coordinates of (0.14, 0.14). These findings demonstrated that side-chain modification can be an effective strategy for developing efficient solution-processable blue light-emitting polymers.