Poly(diarylfluorene) Deep-Blue Polymer Light-Emitting Diodes Based on Submicrometer-Scale Morphological Films Induced by Trace β-Conformation
Lili Sun, Shengjie Wang, Yingying Zheng, Wenyu Chen, Mengyuan Li, Ningning Yu, Yunhao Wang, Jinghao Yang, Yang Xu, Ning Sun, Bin Liu, Xiang An, Lubing Bai, Heyuan Liu, Jinyi Lin, Wei Huang
Abstract
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.