Abstract
Current OLEDs face the problem of unbalanced carrier injection caused by the poor electron mobility. Taking the tunneling concept of superlattice in inorganic semiconductors, we can apply it to the Electron Transporting Layer (ETL) for better electron injection and carrier balance. The fabricated devices, however, show an earlier turn-on voltage and lower device resistance with a huge trade-off of light efficiency. The performance degradation is discussed in the thesis. To begin with, AFM was used to characterize the surface roughness. Surface plasma treatment was investigated to smooth out the surface for process improvement. We also fabricated a series of superlattice structures and examined the thin film thicknesses by Auger Electron Spectrometer (Auger or AES) and Secondary Ion Mass Spectrometer (SIMS.) The superlattice structure comprises alternating 2 to 6 nm-per-layer CuPc/ Alq3 (4 to 12 nm-per-period). Basic design of “ITO/ CuPc(15nm)/ NPB(40nm)/ Alq3(50nm)/ Mg:Ag” was used for reference. The Alq3 layer was then modified with the superlattice in the experiment for comparison. The current-voltage (I-V) diagrams and luminance-current (L-I) diagram were measured and analyzed. We also applied them into single-injected devices and red emitting OLEDs. Same superlattice structures were also used on single-injected devices and red emitting OLEDs for the investigation of carrier injecting status. Finally, we proved that thermal annealing treatment improves the efficiency.