Ultrastable, Deformable, and Stretchable Luminescent Organic-Inorganic Perovskite Nanocrystal-Polymer Composites for 3D Printing and White Light-Emitting Diodes.

Organic-inorganic perovskite nanocrystals with excellent optoelectronic properties have been utilized in various applications, despite their stability issues. The perovskite materials are sensitive to environments such as polar solvents, moisture, and heat. Thus, they are not used for extrusion three-dimensional (3D) printing, as it is usually conducted in the ambient environment and requires heating to liquefy the printed materials. In this work, 11 thermoplastic polymers conventionally used for extrusion 3D printing were investigated to test their capability as protective encapsulation materials for perovskite nanocrystals. Three of them exhibited good protective properties, and one (polycaprolactone, PCL) of these three could be blended with perovskite nanocrystals to form perovskite nanocrystal-PCL composites, which were deformable and stretchable once heated. Because of the low melting point of PCL, the perovskite nanocrystals maintained their optical properties after 3D printing, and the printed objects were still having fluorescent behavior. Moreover, fluorescent micrometer-sized fibers based on the perovskite nanocrystal-PCL composites could also be simply prepared using cotton candy makers. Perovskite nanocrystal-PCL composite films with different emission wavelengths were incorporated with blue light-emitting diodes (LEDs) to realize white LEDs with Commission Internationale de l'Éclairage chromaticity coordinates of (0.33, 0.33).

All-Solution-Processed Red and Orange-Red Organic Light-Emitting Diodes with High-Efficiencies: The Effect of Mixed-Host Emissive Layers and Thermal Annealing Treatment.

The instability of the organic light-emitting diodes (OLEDs) during operation can be attributed to the existence of point defects on the organic layers. In this work, the effect of mixed-host emissive layer and the thermal annealing treatment were investigated to eliminate defects and to boost the device performance. The mixed-host system includes 4,4',4''-tri (9-carbazoyl) triphenylamine (TCTA) and 2,7-bis(diphenylphosphoryl)-9, 9'-spirobi[fluorene] (SPPO13). The mixed-host emissive layer with thermal annealing treatment showed low roughness and few pinholes, and the devices fabricated from this emissive layer exhibited high efficiencies, high stabilities, and long lifetimes. The red and orange-red OLEDs exhibited efficiencies of 13.9 cd/A and 24.35 cd/A, respectively. The longest half-lifetime (L0 =500 cd/m2 ) of the red and orange-red OLEDs were 158 h and 180 h, respectively. Efforts were made to solve problems in large-area coating and to reduce the number of defects on in organic layer. Large-active-area (active area=3 cm×4 cm) red phosphorescent OLEDs (PhOLEDs) devices were realized with very high current efficiency up to 9 cd/A.

Leakage-free solution-processed organic light-emitting diode using a ternary host with single-diode emission area up to 6 × 11.5 cm2.

The electrical current leakage and stability are studied for solution-processed OLEDs with areas of 4.45 mm2, 3 × 3.2 cm2, and 6 × 11.5 cm2. The emission layer of the OLED has a ternary or binary mixed host with hole-transporting molecules tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), together with the electron-transporting molecule 2,7-bis(diphenylphosphoryl)-9,9'-spirobi[fluorene] (SPPO13). The phosphorescent emitters are Ir(mppy)3 for green and bis[4-(4-tert-butylphenyl)thieno[3,2-c]pyridine][N,N'-diisopropylbenamidinato]iridium(iii) (PR-02) for orange. Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) is used as the hole transport layer and PEDOT:PSS is used as the hole injection layer. On top of the emission layer, CsF/Al is deposited by thermal evaporation as the cathode. All organic layers are deposited by blade coating and the initial current leaking defects can be avoided by careful control of the coating conditions. The detrimental burning point caused by a local current short developed after long-time operation can be avoided by reducing the operation voltage using a ternary mixed host. The operation voltage is only 4 V at 100 cd m-2 and 5 V at 250 cd m-2 for the green emitting device. Furthermore, the crystallization defect is reduced by the ternary host. For the orange emitting device, the binary host is good enough with an operating voltage of 5 V at 100 cd m-2. For an area as large as 6 × 11.5 cm2, the OLED shows good stability and there is no burning point after an operation of over 1600 hours.