Large‐Area Blade‐Coated Deep‐Blue Polymer Light‐Emitting Diodes with a Narrowband and Uniform Emission

Abstract

Large‐area polymer light‐emitting diodes (PLEDs) manufactured by printing are required for flat‐panel lighting and displays. Nevertheless, it remains challenging to fabricate large‐area and stable deep‐blue PLEDs with narrowband emission due to the difficulties in precisely tuning film uniformity and obtaining single‐exciton emission. Herein, efficient and stable large‐area deep‐blue PLEDs with narrowband emission are prepared from encapsulated polydiarylfluorene. Encapsulated polydiarylfluorenes presented an efficient and stable deep‐blue emission (peak: 439 nm; full width at half maximum (FWHM): 39 nm) in the solid state due to their single‐chain emission behavior without inter‐backbone chain aggregation. Large‐area uniform blade‐coated films (16 cm2) are also fabricated with excellent smoothness and morphology. Benefitting from efficient emission and excellent printed capacity, the blade‐coated PLEDs with a device area of 9 mm2 realized uniform deep‐blue emission (FWHM: 38 nm; CIE: 0.153, 0.067), with a corresponding maximum external quantum efficiency and the brightness comparable to those of devices based on spin‐coated films. Finally, considering the essential role of deep‐blue LEDs, a preliminary patterned PLED array with a pixel size of 800 × 1000 µm2 and a monochrome display is fabricated, highlighting potential full‐color display applications.

Ultraviolet Organic Laser from Rhombus Microcrystal: Benefits of Single-Molecule Emission from Twisted Structure

“…In the last decades, fluorene-based LOCMs have become the most promising candidates for fabricating ultraviolet and deep-blue OLEDs and organic lasers, associated with their wide bangap (>3.0 eV) and high fluorescence efficiency. ,− Similar to other types of dyes and emitters, with the aim of efficient and stable emission in solid states, two serious defect structures need to be avoided: physical and chemical defects. ,, The former is defined as the intermolecular aggregation and excited states, which may act as the “guest” center with a relatively narrow band to trap exciton from the matrix molecules. ,, The latter involves chemical oxidation and molecular degradation in the material preparation and long-time device operation . These factors lead to low efficiency and alter color purity in the ultraviolet and deep-blue fluorene-based LOCMs. ,,, Then, introducing the bulky units at the 9-position of fluorene can effectively not only enhance the chemical stability and antioxidation to suppress the undesirable green-band emission but also avoid the serious intermolecular aggregation to reduce the formation of multiexcited states, which is a universal strategy to design and prepare efficient and stable ultraviolet and deep-blue LOCMs. ,− Fortunately, a robust deep-blue fluorene molecule (LD-1, as shown Figure d) is obtained with a high emission efficiency (60%), which also showed a lasing behavior at 390 and 410 nm in the single-crystal states, associated with their typical herringbone molecular packing mode. , In fact, the LD-1 single-crystal presents a red-shifted emission of about 20 nm, compared to their diluted solution, due to their relatively planar conformation in the crystal state. More interestingly, herein, an ultraviolet lasing behavior (379 nm) is obtained from the CL-1 single crystal.…”