Inverted organic light-emitting diodes (IOLEDs) have drawn considerable attention for use in active-matrix OLED (AMOLED) displays because of their easy integration with n-channel metal-oxide-based thin film transistors (TFTs). The most crucial issue for IOLEDs is the poor electron injection caused by the bottom cathode. According to previous reports, the turn-on voltages of FIrpic-based IOLEDs are within a range from 4 to 8 V. In this study, we focus on developing bottom-emission IOLEDs with low operating voltages through the use of adequate-charge injection materials. We successfully demonstrate a turn-on voltage as low as 3.7 V for blue phosphorescent IOLEDs. The effective electron injection layers (EIL) were constructed by combining an ultrathin aluminum layer, an alkali metal oxide layer and an organic layer doped with alkali metal oxide, allowing for the effective adjustment of the carrier balance in IOLEDs. The peak efficiencies of the IOLEDs reached 15.6%, 31.8 cd/A and 23.4 lm/W. An external nanocomposite scattering layer was used to further improve light extraction efficiency. The IOLEDs equipped with the SiO2 nanocomposite scattering layer respectively provided performance improvements of 1.3 and 1.5 times that of pristine blue phosphorescent IOLEDs at practical luminance levels of 100 cd/m2 and 1000 cd/m2. Through sophisticated EIL and external light-extraction structures, we obtained blue phosphorescent IOLEDs with satisfactory efficiency and low operation voltages, thereby demonstrating the great potential of nanocomposite film for application in IOLEDs.
For the lighting purpose, white organic light-emitting devices (OLEDs) need to be operated at a high current density
to ensure an ample flux, which will lead the limited lifespan of the device. This situation could be improved through
diversified light-extraction methods. In this study, transparent photoresist mixed with titanium oxide (TiO2)
nanoparticles of different sizes could be utilized to form an internal extraction structures between the indium-tin-oxide
and glass substrate and thereby the out-coupling efficiency of white OLEDs could be significantly improved by this
sophisticated device architecture engineering. The high refractive index of TiO2 is essentially operative for increasing the
refractive index of nanocomposite film and thus diminishing the total internal reflection between the interfaces. In
addition, the nanoparticles served scattering function to multiply the ratio of the substrate and radiation modes. By
employing nanocomposite substrate with mixed dual-sized nanoparticles, we obtained external quantum efficiencies of
the white phosphorescent OLEDs that were about 1.6 times higher than that of the control device at the high
luminescence of 104 cd/m2.
Normally metallic films are required for solar energy and display related coatings. To increase the absorbing
efficiency or contrast, it is necessary to apply an antireflection coating (ARC) on the metal substrate. However, the
design of a metal substrate is very different from the design of a dielectric substrate, since the optical constant of metallic
thin film is very dependent on its thickness and microstructure. In this study, we design and fabricate ARCs on Al
substrates using SiO2 and Nb2O5 as the dielectric materials and Nb for the metal films. The ARC successfully deposited
on the Al substrate had the following structure: air/SiO2/Nb2O5/Metal/Nb2O5/Al. The measured average reflectance of
the ARC is less than 1% in the visible region. We found that it is better to use a highly refractive material than a low
refractive material. The thickness of the metallic film can be thicker with the result that it is easier to control and has a
lesser total thickness. The total thickness of the ARC is less than 200 nm. We successfully fabricated a solar absorber
and OLED device with the ARC structure were successfully fabricated.