Poly(diarylfluorene) Deep-Blue Polymer Light-Emitting Diodes Based on Submicrometer-Scale Morphological Films Induced by Trace β‑Conformation

The hierarchical structure of light-emitting conjugated polymers (LCPs) is the key factor to dominate the ultrafast photoexcitation dynamic behavior and further control the optoelectronic property of their light-emitting devices. Optimizing the submicrometer-scale structure by conformational transition in the amorphous film state is an effective strategy to improve the excitonic behavior and enhance singlet emission efficiency toward fabricating deep-blue polymer light-emitting diodes (PLEDs). Herein, we demonstrate a series of submicrometer-scale morphological films of poly­(diarylfluorene) (PODPF) via tuning the formation of a planar (β) conformation and interchain rearrangement under film pre- and post-treatment. Four types of PODPF films are prepared via spin coating, post-solvent vapor annealing (SVA), post-thermal annealing (TA), and pregelation (GEL) processing, which present variable submicrometer-scale morphologies with trace β-conformation. Compared to the relatively amorphous pristine and GEL films with a weak interchain interaction, PODPF@SVA and PODPF@TA films exhibit an excellent anisotropic fluorescence behavior and efficient deep-blue emission, which are closely associated with the trace β-conformation formation. Finally, PLEDs based on the PODPF@SVA film exhibit an excellent deep-blue emission with a high external quantum efficiency (EQE) of 1.36% and Commission Internationale de l’Elcairage (CIE) coordinates of (0.17, 0.12), which are attributed to the synergistic effect of the formation of the submicrometer structure and trace β-conformation.