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Recently, tremendous progress has been made toward the application of organic light-emitting diodes (OLEDs) in full color flat panel displays and other devices. This article reviews and discusses our recent progress in extended development of emissive semi-interpenetrating polymer networks (E-semi-IPNs) and hybrid quantum dots (QDs)–polymer nanocomposites for use in multicolor and multilayer OLED pixels through low-cost solution processing. Our semi-IPNs with high solvent resistance, containing an inert polymer network and conjugated polymers, served in different layers of OLED devices. These semi-IPNs do not require complicated chemical modification to OLED materials; therefore, many state-of-the-arts conjugated polymers can be utilized to achieve red–green–blue and white OLEDs by tuning formulations. Our research findings on hybrid QD–oligomer nanocomposites lead to the successful design and synthesis of QD–polymer hybrid nanocomposites, which were used to build proof-of-the-concept devices showing good promise in providing excellent color purity and stability from QDs and solution processability from hybrid nanocomposites.
α-Fe2O3 nanorod arrays were fabricated by a low-temperature aqueous chemical growth (ACG) technique and followed by an annealing process. For the surface doping of α-Fe2O3 nanorods, β-FeOOH nanorods obtained via ACG were coated with a thin layer of Cr3+ precursor solution by spin coating, and then underwent the annealing treatment in air. Conducting polymer polypyrrole (PPy) decorated α-Fe2O3 nanorods were prepared by electrodeposition method using malic acid contained pyrrole aqueous solution. Primary results showed that the photocurrents of α-Fe2O3 nanorod array photoanodes were greatly enhanced by surface doping of Cr3+, as well as PPy decoration. This might be due to the retarded charge recombination and promoted surface reaction rate of photogenerated holes with water. Further investigation on surface modification of α-Fe2O3 nanorod array photoanodes is currently conducted in our group.
Recently, tremendous progress has been made toward application of organic (small molecule/polymer) light-emitting diodes (OLEDs) in full color flat panel displays and other devices. However, with current technologies, OLEDs are still struggling with high manufacturing costs which really limit the size of OLEDs panels and with life time, especially differential aging of colors. To be more cost-effective for fabricating OLEDs, we believe solution-processing would be an attractive path due to its simplicity and highly reduced equipment costs. This proceeding paper discusses our recent progress in development of new polymer systems that are highly solvent-resistant but maintaining their photophysical properties and hybrid quantum-dots (QDs)-polymer nanocomposites for their use in multicolor and multilayer OLEDs pixels through solution-processing. Our new polymer systems are named conductive semi-interpenetrating polymer networks (C-Semi-IPNs) served in different layers of OLEDs devices, containing an inert polymer network and conducting polymer(s) including hole transport and emissive materials. Since these do not require complicated chemical modification or introduction of reactive moieties to OLED materials, many state-of-the-arts emissive polymers can be utilized to achieve RGB and white OLEDs. The research findings on hybrid QDoligomer nanocomposite as a good analogue lead to the successful design and synthesis of QDpolymer nanocomposites which were used to build proof-of-the-concept devices showing a good promise in providing excellent color purity and stability as well as device robustness.
Pulsed laser deposition (PLD) has been applied to fabricate thin films of a variety of materials. However, formation of micron-sized particulates during conventional nanosecond laser-based deposition process makes it unsuitable for growing high quality nanoscale materials. Owing to a nonequilibrium non-thermal ablation mechanism and characterized by their short pulse duration compared to thermal diffusion time (tens of picoseconds), ultrafast laser pulses are able to produce particulate-free precursor vapor for nanoscale material deposition. In this article, the foundation of non-thermal ultrafast laser ablation will be examined by both experimental and theoretical investigations. Ultrafast laser-induced high-density electron ejection and subsequent build -up of a strong electric field above the target material were observed. Mass spectrometry and electron microscopy measurements confirmed the particulate-free nature of ultrafast laser ablation. Using ultrafast laser-based particulate-free PLD approach, high quality ZnO nanowires were grown on sapphire and silicon substrates. The optical properties of ZnO nanowires, including the external and internal quantum efficiency of nanowire nanolasers, were experimentally determined. In addition, a nanowire UV photodiode based on p−Si/n−ZnO nanowires was successfully fabricated. This first nanowire photodiode device shows good photocurrent characteristics when operated under reverse bias.
We have studied the temperature dependence of CER spectra of layered InGaAs QWRs and QDCs and found strain-induced splitting of lh and hh states occur in both InGsAs and GaAs layers. By fitting experimental data using Varshni law and Bose-Einstein type relation, various parameters are obtained, which are similar to those of bulk GaAs. We pointed out that a caution must be excised when extracting the electron-phonon interaction parameters by subtracting the thermal dilation part from the experimental data of the embedded semiconductor microstructures because in these structures the temperature-induced lattice-dilation may produce additional strain besides the lattice mismatch.