Organic light emitting diodes (OLEDs) for lighting
by Xiaoming Yu
Ph.D. Electronic and Computer Engineering
xxii, 170 p. : ill. ; 30 cm
OLEDs have the advantages of self-emitting, fast response time, ultra-high contrast ratio, etc.. OLEDs have become the most attractive technology in the display and the lighting fields. This thesis researched new methods of developing good performance white emission OLEDs (WOLEDs) in the lighting application. 32+6–3...[ Read more ]
OLEDs have the advantages of self-emitting, fast response time, ultra-high contrast ratio, etc.. OLEDs have become the most attractive technology in the display and the lighting fields. This thesis researched new methods of developing good performance white emission OLEDs (WOLEDs) in the lighting application.
New yellow emission phosphorescent materials were developed. The best optimization case was 5% Ir(DPA-Flpy)3 doped into CBP as the emission layer. The emission peak was 562 nm. The best efficiency of bottom emission device was 31cd/A. Charged complexes [Ir(L)2(N-N)]+(PF6–) were also fabricated as yellow emission materials with high efficiency 19.7cd/A. The best performance yellow emission material Ir(DPA-Flpy)3 was used in simple fabricated white organic light emission diodes (WOLEDs). Ultra-thin carrier limitation layer was used in the device structure for balancing the hole and electron distributions. After structure optimization in multi-emission-layer WOLEDs device, the device highest efficiencies reach 23 cd/A. The CIE coordinates could be stably controlled within 0.015, and CRI was 86 at normal direction and 87 at 80 degrees off the normal.
Top emitting architecture has advantageous in high resolution active matrix OLEDs to enhance the aperture ratio and of being applied as backlighting LCDs. Aluminum direct anode TOLEDs were fabricated compatible with MOS or TFT driving technology. The optimization thickness for V2O5 buffer layer was 5nm, with which the efficiency of green aluminum anode TOLEDs could be enhanced over twice. The efficiency of WTOLEDs was 23.4cd/A. TOLEDs on silicon were fabricated. Aluminum directly on silicon was used as anode. Devices were fabricated on silicon substrate without any insulator, which was a great improvement in fast heat radiation. Phosphorescent green emission device had the highest brightness 120,000cd/m2, 1.7 times the value of standard bottom emission device 70, 000cd/m2. The highest efficiency was 41 cd/A. WOLEDs were also fabricated with the highest efficiency 14 cd/A.
Stainless steel has good flexibility if sheets thickness is under 0.1mm. An electrical-chemical method was applied in polishing s.s. sheet to get TOLEDs substrate with extremely low surface roughness and high reflectivity. After polishing process, mean roughness of polished surface reached 1.93nm. Then TOLEDs were fabricated directly on stainless steel without any additional high work function metal or barrier layer. Green OLEDs performance had almost twice efficiency than the bottom emission devices. TOLEDs on the s.s. substrate had 8 time lifetime than common aluminum TOLEDs. The best WOLEDs on s.s substrate rendered the white light with CRI 94. WTOLEDs on general metal substrats such as Al sheets were also fabricated.