Large‐Area Deep‐Blue Polymer Light‐Emitting Diodes with Well‐Resolved Emission from Planar Conformational Segments Fabricated via Brush Coating

Abstract The fabrication of large‐area printed deep‐blue polymer light‐emitting diodes (PLEDs) is a prerequisite for solid‐state lighting and flat‐panel displays. However, manufacturing large‐area narrow‐band deep‐blue PLEDs remains a challenging task owing to the difficulties in reducing structural distortions caused by the transitions from the ground to excited states. Herein, large‐area deep‐blue PLEDs with narrow‐band emission from the planar (β) conformational segments of polydiarylfluorenes are fabricated via brush coating. First, large‐area uniform brush‐coated films (4 × 4 cm²) with a relatively smooth morphology are manufactured. They produce strong, stable, and narrow‐band deep‐blue emission (full width at half maximum (FWHM): 29 nm for the 0–0 and 0–1 emission peaks), which results from single β‐conformational segments without a charge transfer state. Therefore, owing to their efficient emission and excellent printing capability, large‐area brush‐coated PLEDs with an emission area of 3 × 3 cm² and uniform deep‐blue emission (FWHM: 27 nm; CIE chromaticity coordinate: (0.15, 0.10), brightness: 3780 cd m⁻²) are obtained, and their maximum external quantum efficiency (1.79%) is two times higher than those of the devices containing spin‐coated films. Finally, considering the key role of deep‐blue PLEDs, the fabrication of a preliminary patterned PLED array confirms their potential display applications.