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).
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.
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