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

Intrinsically stretchable fully π-conjugated polymers with inter-aggregate capillary interaction for deep-blue flexible inkjet-printed light-emitting diodes

Fully π-conjugated polymers consisting of plane and rigid aromatic units present a fantastic optoelectronic property, a promising candidate for printed and flexible optoelectronic devices. However, obtaining high-performance conjugated polymers with an excellent intrinsically flexible and printable capacity is a great challenge due to their inherent coffee-ring effect and brittle properties. Here, we report an asymmetric substitution strategy to improve the printable and stretchable properties of deep-blue light-emitting conjugated polymers with a strong inter-aggregate capillary interaction for flexible printed polymer light-emitting diodes. The loose rod-shaped stacking of asymmetric conjugated polymers chain in the precursor printed ink makes it easier to improve the intrinsic stretchability of inkjet-printed films. More interestingly, the anisotropic shape rod-like aggregate of conjugated polymers chains also induced a strong capillary interaction and further suppressed the coffee-ring effect, which is more likely to allow for uniform deposition during printed processing and form uniform printed films.

Plasticizer Design Principle of "Like Dissolves Like": Semiconductor Fluid Plasticized Stretchable Fully π-Conjugated Polymers Films for Uniform Large-Area and Flexible Deep-Blue Polymer Light-Emitting Diodes

Physical blending of fully π-conjugated polymers (FπCPs) is an effective strategy to achieve intrinsically stretchable films for the fabrication of flexible optoelectronic devices, but easily causes phase separation, nonuniform morphology and uncontrollable photo-electronic processing. This may cause low efficiency, unstable and nonuniform emission, and poor color purity, which are undesirable for deep-blue flexible polymer light-emitting diodes (FPLEDs). Herein, a "Like Dissolves Like" design principle to prepare semiconductor fluid plasticizers (SFPs) is established and intrinsically stretchable FπCPs films via external plasticization for high-performance deep-blue FPLEDs are developed. Three fundamental requirements are proposed, "similar conjugated skeleton, similar molecular polarity, and similar electronic structures," to prepare model-matched nonpolar M1 and polar M2 plasticizers for poly(9,9-dioctylfluorene) (PFO). Large-area plasticized PFO films exhibit an efficient, narrowband, and stable ultra-deep-blue electroluminescence (FWHM < 40 nm, CIE: 0.12, 0.04), uniform morphology, and excellent intrinsic stretchability (fracture strain >20% and crack-onset strain >120%). Efficient and uniform deep-blue FPLEDs based on stretchable PFO films are fabricated with a high brightness of ≈3000 cd cm-2. Finally, blended PFO films exhibit outstanding stretch-deformation cycling stability of their deep-blue electroluminescent behavior, confirming the effectiveness of the "Like Dissolves Like" principle to design matched SFPs for stretchable FπCP films in flexible electronics.

Triphenylamine Spirofunctionalized Light-Emitting Conjugated Polymer with an Ultradeep-Blue Narrowband Emission for Large-Area Printed Display

Emerging printed large-area polymer light-emitting diodes (PLEDs) are essential for manufacturing flat-panel displays and solid lighting devices. However, it is challenging to obtain large-area and stable ultradeep-blue PLEDs because of the lack of light-emitting conjugated polymers (LCPs) with robust deep-blue emissions, excellent morphological stabilities, and high charging abilities. Here, a novel unsymmetrically substituted polydiarylfluorene (POPSAF) is obtained with stable narrowband emission for large-area printed displays via triphenylamine (TPA) spirofunctionalization of LCPs. POPSAF films show narrowband and stable ultradeep-blue emission with a full width at half maximum (FWHM) of 36 nm, associated with their intrachain excitonic behavior without obvious polaron formation. Compared to controlled poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF), excellent charge transport is observed in the POPSAF films because of the intrinsic hole transport ability of the TPA units. Large-area PLEDs are fabricated via blade-coating with an emission area of 9 cm2, which exhibit uniform ultradeep-blue emission with an FWHM of 36 nm and corresponding Commission internationale de l'éclairage (CIE) coordinates of (0.155, 0.072). These findings are attributed to the synergistic effects of robust emission, stable morphology, and printing capacity. Finally, preliminary printed passive matrix (PM) PLED displays with 20 × 20 pixels monochromes are fabricated, confirmed the effectiveness of spirofunctionalization in optoelectronics.

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

Light-emitting molecular crystals with efficient emission behavior are crucial for fabricating low-threshold ultraviolet organic lasers. Herein, we demonstrated a rhombus microcrystal from a fluorene-based conjugated molecule (CL-1) with robust emission behavior for an ultraviolet organic laser. Due to the synergistic effect of twisted intramolecular conformation and weak π-interaction, the CL-1 single crystal showed an extremely high photoluminescence quantum yield (PLQY) of ∼82%, due to their single-molecule excitonic behavior. Considering the diverse noncovalent interactions, CL-1 molecules easily self-assembled into the rhombus microcrystals. Finally, a low-threshold ultraviolet organic laser was fabricated with a sharp emission at 379 nm, attributed to the 0-1 vibration band of a single CL-1 molecule, also further confirming the single twisted-molecule emission in crystal states. Precisely controlling the intramolecular twisted structure and intermolecular interaction of organic conjugated molecules is a precondition to obtain robust ultraviolet emission for optoelectronic applications.