Narrowband Deep-Blue Polymer Light-Emitting Diodes Based on Photolithographable Blend Matrix Emitters

Polyfluorenes (PFs) exhibit enormous potential in blue polymer light-emitting diodes (PLEDs). However, PFs suffer from emitting undesired green emission in solid-state films, which induces emission spectral broadening and significantly deteriorates color purity. In this work, we develop a mixed-host design strategy for the emissive layer to construct directly photolithographic blue PLEDs with narrowband emission. By dispersing poly(9,9-dioctylfluorene) (PFO) into a mixed matrix composed of 1,3-dicarbazol- 9-ylbenzene (mCP) and poly(9-vinylcarbazole) (PVK), the dilution effect of mCP and the steric hindrance effect of PVK synergistically suppress PF aggregation and green emission, realizing narrowband deep-blue luminescence. High-resolution lithographically patterned PLEDs with a pixel size of 5 μm (equivalent to a resolution of 2540 PPI) are successfully fabricated via UV-induced photo-cross-linking between PVK and the photosensitizer. The optimized high-resolution devices deliver a Commission Internationale de l’Éclairage (CIE) coordinate of (0.18, 0.10), a peak external quantum efficiency (EQE) of 2.31%, and a maximum luminance of 1520 cd/m 2 at 9 V. This work provides a feasible and versatile technical strategy for the development of high-color-purity deep-blue and high-resolution PLEDs toward advanced display applications.