Szu-Yi Chen

Stable inverted bottom-emitting organic electroluminescent devices with molecular doping and morphology improvement

Stable inverted bottom-emitting organic light-emitting diodes (IBOLEDs) have been investigated by inserting n-type Cs2O dopant between indium-tin oxide bottom cathode and Alq3, the combination of which not only improved the morphology of organic layer but enhanced the lifetime of the IBOLED. This n-type doped IBOLED achieved efficiencies of 5.2cd∕A and 2.0lm∕W at 20mA∕cm2. The 20% decay lifetime (t80) of Cs2O doped IBOLED is 270h which is about 1.7 times more stable than that of the conventional OLED (160h) and 2.5 times of Li doped IBOLED (104h).

Highly efficient and stable inverted bottom-emission organic light emitting devices

The authors report the development of highly efficient and stable C545T doped green fluorescent Alq3 inverted bottom-emission organic light emitting device (OLED), with a device configuration of ITO∕Mg∕Cs2O:Bphen∕Alq3∕C545T:Alq3∕NPB∕WO3∕Al, that achieved a maximum current efficiency of 23.7cd∕A and a power efficiency of 12.4lm∕W which are two times better than those of the conventional OLED. At a brightness level of 100cd∕m2, the device required driving current density only as low as 0.5mA∕cm2 at a driving voltage of only 5.0V and its half-lifetime T1∕2 in excess of 104000h.

Ultrathin Electron Injection Layer on Indium–Tin Oxide Bottom Cathode for Highly Efficient Inverted Organic Light-Emitting Diodes

We have fabricated a highly efficient inverted bottom-emission organic light-emitting diode (IBOLED) based on an indium–tin oxide (ITO) bottom cathode deposited with an ultrathin 1 nm layer of Mg to promote electron injection. The threshold voltage of this IBOLED with a structure of ITO/Mg/Alq3/NPB/WO3/Al was 4.2 V and an efficiencies of 4.66 cd/A and 1.51 lm/W were achieved at an operational voltage of 8.9 V and a brightness of 940 cd/m2. In comparison with an ITO/Alq3 bottom cathode composition, a reduction in drive voltage from 13.8 to 7.8 V in voltage was obtained at 1 mA/cm2. A charge-transfer dipole model is proposed to rationalize the enhanced electron injection.

Comparative study of single and multiemissive layers in inverted white organic light-emitting devices

The authors have fabricated and compared highly efficient inverted white organic light-emitting devices (WOLEDs) with a single emission layer (SEL) and with a multiemission layer (MEL). The efficiency levels of the WOLEDs with a SEL and a MEL achieved 13.0cd∕A, 10.6lm∕W and 11.3cd∕A, 7.3lm∕W, respectively. The projected half lifetime of a SEL device under an initial luminance of 400cd∕m2 is expected to be over 34000h, which is five times better than that of a MEL device of 6350h. The Commission International de l’Eclairage coordinates of a SEL device are not affected by aging.

Lasing characteristics at different band edges in GaN photonic crystal surface emitting lasers

We have investigated the lasing characteristics of GaN-based two-dimensional photonic crystal surface emitting lasers (PCSELs) with different PC lattice constants by using angled resolved spectroscopy. Due to the Bragg diffraction theory, normalized frequency of lasing wavelength of PCSELs can be exactly matched with three distinct band-edge frequencies (Γ1, K2, and M3) in the photonic band diagram. The three band-edge frequencies (Γ1, K2, and M3) have different emission angles corresponding to the normal direction of the sample (0°, 29°, and 59.5°).

29.2: Highly Efficient and Stable Inverted Bottom-Emission Organic Light Emitting Devices

We report the development of highly efficient and stable C-545T doped green fluorescent Alq inverted bottom-emission OLED (IBOLED) which achieved a maximum efficiency of 22.2 cd/A and 12.4 lm/W with an projected t1/2 of 30,000 h with L0 = 100 cd/m2. The DSA-Ph doped MADN sky blue fluorescent IBOLED device had a maximum efficiency of 12.7 cd/A and 7.6 lm/W. At a brightness level of 100 cd/m2, these green and blue IBOLED devices require drive current densities only as low as 0.5 and 0.9 mA/cm2, respectively.

The lasing characteristics of GaN-based two-dimensional photonic crystal surface-emitting lasers

GaN-based photonic crystal surface-emitting lasers(PCSELs) with AlN/GaN distributed Bragg reflectors were fabricated and analyzed. Different lasing characteristics of GaN-based PCSEL has been determeined and demonstrated by the PC lattice constants. The laser emission behavior covered the whole PC patterns of 50 μm in diameter. Under the optical pumping at room temperature, the PCSEL with PC lattice constant of 230nm shows a threshold energy density of about 2.7 mJ/cm2. Above the threshold, one dominated peak emits at 420.11 nm with a linewidth of 1.1 Å. The lasing wavelength emitted from PC lasers with different lattice constants occurs at the calculated band-edges provided by the PC patterns which further shows different polarization angles due to the light diffracted in specific directions, corresponding exactly to Γ, K, and M directions in the K-space. The PCSEL also shows a characteristic temperature of 148K and a spontaneous emission coupling efficiency β of about 5x10-3. Besides, the coupled-wave model in the PC hexagonal-lattice is applied to distinguish the discrepancy in threshold power and the corresponding coupling coefficient. The results show the lasing actions within Γ, K, and M modes have the substantial relation between the threshold energy density and the coupling coefficient.

Blue GaN-based vertical cavity surface emitting lasers by CW current injection at 77K

In the paper, we describe the fabrication and performance characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs) by optical pumping and current injection. According to the employment of high-quality and high-reflectivity AlN/GaN DBRs in the whole structure, the lasing action of optically pumped GaN-based VCSELs with hybrid mirrors has been observed at room temperature. Due to the excellent results of optically pumped GaN-based VCSELs with hybrid mirrors, we further demonstrated the lasing behavior of GaN-based VCSELs by continuous-wave current injection at 77 K. The laser has one dominated blue wavelength located at 462 nm with a linewidth of about 0.15 nm and the threshold injection current at 1.4 mA. The divergence angle and polarization ratio of the GaN-based VCSELs with hybrid mirrors are about 11.7° and 80%, respectively. A larger spontaneous coupling efficiency of about 7.5×10-2 was also measured.