Anna B. Chwang

Thin film encapsulated flexible organic electroluminescent displays

We describe encapsulated passive matrix, video rate organic light-emitting diode (OLED) displays on flexible plastic substrates using a multilayer barrier encapsulation technology. The flexible OLED (FOLED™) displays are based on highly efficient electrophosphorescent OLED (PHOLED™) technology deposited on barrier coated plastic (Flexible Glass™ substrate) and are hermetically sealed with an optically transmissive multilayer barrier coating (Barix™ encapsulation). Preliminary lifetime to half initial luminance (L0∼100 cd/m2) of order 200 h is achieved on the passive matrix driven encapsulated 80 dpi displays; 2500 h lifetime is achieved on a dc tested encapsulated 5 mm2 FOLED test pixel. The encapsulated displays are flexed 1000 times around a 1 in. diameter cylinder and show minimal damage.

Graded mixed-layer organic light-emitting devices

We describe the performance of graded, mixed-layer organic light- emitting devices (OLEDs). The devices are step graded from a mostly hole transporting layer (HTL) to a mostly electron transporting layer (ETL) from anode side to cathode side, respectively. Luminous efficiencies of >4.5 lm/W and 10 cd/A are obtained at 1000 cd/m2 for green, electrofluorescent, graded mixed OLEDs. These efficiencies are significantly higher than those of a uniformly mixed device, i.e., a device in which the HTL and ETL are uniformly mixed, but lower than those of a conventional heterostructure device employing the same dopant material. The operating lifetime of the graded mixed OLEDs, however, is much improved over the heterostructure device. The results of our work suggest that the graded mixed OLED device structure represents a path to achieving extended lifetimes with sufficient efficiency for flat panel display applications in which this parameter is critical to market acceptance.

Operational stability of electrophosphorescent devices containing p and n doped transport layers

The operational stability of low-operating voltage p-i-n electrophosphorescent devices containing fac-tris(2-phenylpyridine) iridium as the emissive dopant is investigated. In these devices, Li-doped 4,7-diphenyl-1,10-phenanthroline (BPhen) served as an n-type electron transport layer, or as an undoped hole blocking layer (HBL), and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane doped 4,4′,4″-tris(3-methylphenylphenylamino) triphenylamine served as a p-type hole transport layer. The glass transition temperature of BPhen can be increased by the addition of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq), resulting in improved morphological stability, thereby reducing device degradation. When thermally stable BAlq was used as a HBL in both p-i-n and undoped devices, the extrapolated operational lifetime (normalized to an initial luminance of 100 cd/m2) of the p-i-n and undoped devices are 18 000 and 60 000 h, respectively, indicating that the presence of p and n dopants can accelerate...

Temperature and gate voltage dependent transport across a single organic semiconductor grain boundary

Temperature and gate voltage dependent transport measurements on single grain boundaries in the organic semiconductor sexithiophene (6T) are described. Isolated grain boundaries are formed by vacuum deposition of pairs of 6T grains between Au electrodes 1.5–2.0 μm apart on SiO2/Si substrates; grain boundary formation is monitored using atomic force microscopy. The Si substrate serves as the gate electrode. We show from the activation energy, threshold voltage, and field effect resistance of the grain boundary junction that carrier transport is limited by the grain boundary. The activation energy of room temperature transport is of the order of 100 meV at carrier densities of ∼1018 cm−3 and decreases with increasing carrier concentration (gate voltage). We also observe that longer grain boundaries with smaller misorientation angles result in larger currents through a grain boundary. We relate our data to two models, one that assumes acceptor-like traps localized at a grain boundary and another that assumes...

64.2: Full Color 100 dpi AMOLED Displays on Flexible Stainless Steel Substrates

We demonstrate full color, top emission, active matrix OLED displays on flexible stainless steel substrates. The 100 dpi QVGA displays are driven by LTPS TFT backplane with excimer laser annealed poly-Si. To our knowledge this is the worlds highest resolution full color flexible AMOLED display on steel foil demonstrated to date. Encapsulation is by a multilayer thin film.

Flexible OLED display development: Strategy and status

— In this paper, the current status of flexible OLED (FOLED®) display development will be reviewed, including previous results for passive-matrix displays on plastic and current progress on active-matrix displays on steel foil. The displays incorporate high-efficiency small-molecule phosphorescence OLED (PHOLE™) technology. The ultimate goal is to develop high-information-content high-performance long-lived, and large-area FOLED displays that can be pulled or rolled out from a smaller pen-like housing. The strategy for achieving this goal will be presented.

21.4: Thin Film Encapsulated Flexible OLED Displays

Fully encapsulated passive matrix, video rate, phosphorescent OLED displays on flexible plastic substrates using a multilayer barrier encapsulation technology are described. The flexible OLED (FOLED™) displays are based on highly efficient electrophosphorescent OLED (PHOLED™) technology deposited on barrier coated plastic film (Flexible Glass™ substrate) and are hermetically sealed with an optically transmissive multilayer barrier coating (Barix™ Encapsulation). Preliminary lifetime to half initial luminance (Lo∼100 cd/m2) of order 200 h is achieved on the encapsulated 80 dpi displays using a passive matrix drive at room temperature; 2500 h lifetime is achieved on a dc tested encapsulated 5 mm2 FOLED test pixel. The encapsulated displays are flexed 1000 times around a 1″ diameter cylinder and show minimal damage.

49.3: A 200‐dpi Transparent a‐Si TFT Active‐Matrix Phosphorescent OLED Display

We have fabricated a 120×160 high-resolution (200dpi) a-Si TFT active-matrix transparent phosphorescent OLED (PHOLED™) display with novel pixel architecture to maximize transparency and aperture ratio and also ensure comparable light emission from both sides of the display. The a-Si backplane was selected as the technology that would most easily enable the pathway toward achieving high-resolution flexible transparent AMOLEDs (T-AMOLEDs) on polymeric substrates. A-Si TFTs are preferred for fabrication on polymeric substrates since lower process temperatures can be used in comparison to poly-Si TFT processes. As a TOLED generally emits less light from a transparent cathode than anode, a standard 2T pixel was designed with both an opaque, reflective anode region on top of the TFTs as well as a conventional transparent ITO anode to equal the emission from both contacts. This design achieves a total pixel aperture ratio of 64% with a display transparency of 23% in the off-state.

Graded mixed-layer OLEDs

We describe the performance of mixed-layer, small molecule organic light-emitting devices (OLEDs) that are step-graded from a mostly hole transporting layer (HTL) to a mostly electron transporting layer (ETL) from anode-side to cathode-side, respectively. The devices are based on a green, electrofluorescent dopant and achieve luminous efficiencies of > 4.5 lm/W and 10 cd/A. These efficiencies are significantly higher than those of a uniformly mixed device, i.e., a device in which the HTL and ETL are uniformly mixed, but lower than those of a conventional heterostructure device employing the same dopant material. Operating lifetime of the graded mixed OLEDs, however, is much improved over the heterostructure device. We then compare the performance of fluorescent OLEDs at high current drive to that of phosphorescent OLEDs at high current drive in the context of passive matrix driven display suitability.

Flexible phosphorescent OLEDs on metal foil for military and commercial applications

We report recent advances in the development of low power consumption, emissive, flexible active matrix displays through integration of top emitting phosphorescent OLED (T-PHOLED) and poly-Si TFT backplane technologies. The displays are fabricated on flexible stainless steel foil. The T-PHOLEDs are based on UDC phosphorescent OLED technology, and the backplane is based on PARCs Excimer Laser Annealed (ELA) poly-Si TFT process. We also present progress in operational lifetime of encapsulated T-PHOLED pixels on planarized metal foil and discuss PHOLED encapsulation strategy.