Tukaram K. Hatwar

Triplet annihilation exceeding spin statistical limit in highly efficient fluorescent organic light-emitting diodes

We have demonstrated that the exemplary red fluorescent organic light-emitting diodes (OLEDs) gain as much as half of their electroluminescence from annihilation of triplet states generated by recombining charge carriers. The magnitude of triplet-triplet annihilation (TTA) contribution in combination with the remarkably high total efficiencies [>11% external quantum efficiency (EQE)] indicates that the absolute amount of electroluminescence attributable to TTA substantially exceeds the limit imposed by spin statistics, which was independently confirmed by studying magnetic field effects on delayed luminescence. We determined the value of 1.3 for the ratio of the rate constants of singlet and triplet channels of annihilation, which is indeed substantially higher than the value of 0.33 expected for a purely statistical annihilation process. It is, however, in an excellent quantitative agreement with the extent of the experimental contribution of delayed luminescence to steady-state electroluminescence. The ...

System considerations for RGBW OLED displays

Abstract— The fabrication of full-color RGBW OLED displays using a white emitter with RGB color filters has been previously described. This paper discusses the effect of several display-system factors on the important RGBW OLED display performance attributes of power consumption, lifetime, and perceived image quality. These display-system factors include the spectrum of the white OLED, the white OLED structure, the color-filter selection, the subpixel aperture ratios, and the pixel arrangement (including sub-sampling).

4.3: Lifetime- and Power-Enhanced RGBW Displays Based on White OLEDs

In this paper, we describe techniques for improving the power consumption and lifetime of full-color AMOLED displays with an RGBW pixel format. A highly efficient and stable white OLED, with color optimized for the display white point (D65) has been developed, which enables low power consumption as well as stable emission. Additionally, a novel approach for improving the lifetime of RGBW displays using subsampled R and B subpixels is discussed.

Full-color AMOLED with RGBW pixel pattern

Abstract— A full-color AMOLED display with an RGBW color filter pattern has been fabricated. Displays with this format require about one-half the power of analogous RGB displays. RGBW and RGB 2.16-in.-diagonal displays with average power consumptions of 180 and 340 mW, respectively, were characterized for a set of standard digital still camera images at a luminance of 100 cd/m2. In both cases, a white-emitting AMOLED was used as the light source, and standard LCD filters were used to provide the R, G, and B emission. The color gamuts of these displays were identical and the higher overall efficiency of the RGBW format results from two factors. First, a large fraction of a typical image is near neutral in color and can be reproduced using the white sub-pixel. Second, the white sub-pixel in an RGBW AMOLED display is highly efficient because of the absence of any color filter. The efficiency of these displays can be further enhanced by choosing a white emitter optimized to the target display white point (in this case D65). A two-emission layer configuration based upon separate yellow and blue-emitting regions is shown to be well suited for both the RGBW and RGB formats.

Coercivity enhancement of Co/Pt superlattices through underlayer microstructure modification

A major effort is directed toward increasing the coercivity of Co/Pt superlattice films for practical applications. We have used amorphous ITO as the underlayer and have studied the microstructure and magnetic properties of Co/Pt multilayer film by varying the deposition conditions of the underlayer. We have correlated observed microstructural features with coercivity and squareness behavior. A smooth underlayer deposited at low pressure results in high squareness but low coercivity, whereas a rough underlayer deposited at high pressure produces Co/Pt films with low squareness but high coercivity. We attribute the increase in coercivity to a decrease in Co/Pt columnar diameter and to enhanced domain wall pinning because of morphology-induced micro-structural defects such as irregular interfacial and columnar boundaries, and a decrease in columnar diameter. The concurrent reduction in squareness is attributed to a decrease in anisotropy because of degraded crystallinity and admixture of fcc(200) texture. Underlayer morphology can be easily controlled by sputtering pressure for the optimum combination of coercivity and squareness.

8.2: Development of Tandem White Architecture for Large‐Sized AMOLED Displays with Wide Color Gamut

In this paper, we discuss the development of tandem white OLED structures optimized for TV-Sized full-color AMOLED displays using an RGBW pixel format. A highly efficient (24 cd/A) and stable tandem white OLED, with color optimized for the display white point (D65), has been developed that enables low power consumption ( 100K h). Additionally, we describe the development of new color filters that deliver 102% NTSC ratio when combined with the tandem white OLEDs.

System design for a wide‐color‐gamut TV‐sized AMOLED display

Abstract— By using current technology, it is possible to design and fabricate performance-competitive TV-sized AMOLED displays. In this paper, the system design considerations are described that lead to the selection of the device architecture (including a stacked white OLED-emitting unit), the backplane technology [an amorphous Si (a-Si) backplane with compensation for TFT degradation], and module design (for long life and low cost). The resulting AMOLED displays will meet performance and lifetime requirements, and will be manufacturing cost-competitive for TV applications. A high-performance 14-in. AMOLED display was fabricated by using an in-line OLED deposition machine to demonstrate some of these approaches. The chosen OLED technologies are scalable to larger glass substrate sizes compatible with existing a-Si backplane fabs.

52.2: Hybrid Tandem White OLEDs with High Efficiency and Long Life‐time for AMOLED Displays and Solid‐State Lighting

Excellent performance (61 cd/A efficiency, 27% EQE, 6.2 V, 6500 K white point, 35,000 h half-life) was obtained using 2-stack hybrid tandem white OLED. This is >70% EQE improvement over the all-fluorescent tandem white resulting in >30% reduction in power consumption for a 32″ AMOLED HDTV. Hybrid Tandems for lighting show EQE between 28.4 and − 30.6%, and lifetime between 70,000 and 125,000 h without outcoupling.

Effect of argon sputtering pressure on the magnetic properties and morphology of TbFeCo films

The effect of argon sputtering pressure on the magnetooptic and structural properties of TbFeCo amorphous films was investigated. The films were prepared by DC magnetron sputtering from a TbFeCo homogeneous alloy target. At low argon pressures, the Tb concentration in the film was lower than in the target, while at high pressures, the Tb concentration was greater in the film than in the target. The films deposited at low sputtering pressure have high Kerr rotation and reflectivity. The Kerr-hysteresis-loop squareness decreases and slantedness increases with increasing Ar pressure. The films prepared at low Ar pressure were very smooth and without detectable columnar growth. This supports the hypothesis that the columns are not required for the film to possess perpendicular anisotropy. The study indicates that it is possible to increase the performance and stability of the film by choosing appropriate deposition conditions. >

High-performance Co/Pt multilayer magneto-optical disk using ultrathin seed layers

We have prepared high-performance disks based on Co/Pt multilayers using ultrathin seed layers. Both crystalline (such as ZnO) and amorphous [such as indium-tin-oxide (ITO) and Si] materials were used as seed layers. We found that very thin layers of these materials enhance coercivity, squareness of the Kerr loop, and perpendicular anisotropy of the Co/Pt superlattices. These beneficial effects are obtained with a seed layer as thin as 0.2 nm. This is incontrast with the earlier presumptions that indicated much thicker layers, about 80 nm of crystalline material, were required to improve the texture of the Co/Pt multilayer for sufficient enhancement in the coercivity. Further, the data indicated that disks with amorphous seed layers generally have higher perpendicular anisotropy and lower recording noise as compared to those with crystalline ZnO. We have prepared disks using a thin amorphous ITO seed layer and a simple disk structure: grooved PC/ITO/12[Co/Pt]/lacquer overcoat. The performance of these dis...