Yuan-Sheng Tyan

Topics on thin film CdS/CdTe solar cells

Abstract Efficient thin film CdS/CdTe solar cells can be prepared by the close-spaced sublimation technique onto soda-lime glass coated with either indium tin oxide or tin oxide. Oxygen is needed to enhance the p characteristics of CdTe; a high substrate temperature is needed to reduce the interfacial defects at the CdS/CdTe junction. Cells with gold electrodes are not stable owing to AuCdTe interaction. Alternative electrodes to CdTe can be prepared by using a HNO 3 -H 3 PO 4 surface treatment. The cells whoed 30–40% efficiency degradation when aged over 2 years at 100 °C under continuous air mass 1 illumination. The degradation appears to result from a decrease in the carrier concentration with aging. The aging process is not sensitive to ambience but is sensitive to the presence of light or voltage bias. It is believed to be related to the dependence of the effective carrier concentration on the cooling rate subsequent to the CdTe deposition. Defect interaction may be a possible cause of the aging behavior but photoluminescence and deep-level studies have not established the mechanism involved. The evidence suggests that trace impurities can have significant effects on the behavior of the cells and could be responsible for the aging behavior.

60.1: Invited Paper: Tandem Hybrid White OLED Devices with Improved Light Extraction

A high-efficacy white OLED device is reported. At 1,000 cd/m2, the device showed an efficacy of 56 lm/W. The color at (0.387, 0.389) was within the Energy Star tolerance quadrangle; the CRI at 83.6 exceeded the requirements. The device had a tandem hybrid architecture comprising a fluorescent blue-emitting unit and a phosphorescent yellow-red-emitting unit. It also had an internal extraction enhancement structure that greatly enhanced the light extraction efficiency.

54.2: Tandem White OLEDs Combining Fluorescent and Phosphorescent Emission

Tandem white OLEDs with fluorescent and phosphorescent emission have been fabricated. Their electroluminescence performance is dependent on fluorescent blue-emitting portion in a white spectrum. When CIEx = 0.33, CIEy = 0.35, the devices can achieve 22% external quantum efficiency, 50 cd/A, 25 lm/W, and ∼10,000 h lifetime, tested at 6.2 V and 1000 nits. If the blue-emitting portion is reduced to produce color with CIEx = 0.34, CIEy = 0.40, the devices can exhibit ∼23% external quantum efficiency, 57 cd/A, 30 lm/W, and ∼30,000 h lifetime when tested at 5.9 V and 1000 nits.

61.2: Fluorescent White OLED Devices with Improved Light Extraction

An all-fluorescent white OLED device with 14.5% external quantum efficiency and 31.2 lm/W efficacy has been demonstrated. The color coordinate at (0.387, 0.381) falls well within the DOE Energy Star tolerance quadrangle for 4000K CCT. The T50 lifetime is projected to be over 10,000 h at an initial brightness of 1,000 cd/m2. The performance is achieved through the use of improved OLED materials, improved architecture, as well as a light extraction structure that more than doubles the light extraction efficiency.

P-173: Reduction of Shorting Defects in OLED Devices

A method to reduce the detrimental effect of shorting defects in OLED devices is presented. The method involves the application of a transparent thin film of appropriate electrical resistance between two electrodes in order to divert the current away from the shorting defects.

P-178: High-Efficiency Long-Lifetime Phosphorescent OLED Devices Based on Electron-Trapping Iridium (III) Complexes

We have developed new iridium (III) complexes having coumarin, including its aza-analogue structure, in their ligands. These Ir complexes are highly emissive with colors ranging from yellow, yellowish-green to green. Electrochemical analysis shows that the reduction and oxidation potentials of these complexes occur at significantly less negative and more positive potentials, respectively, than are found for typical Ir(III) complexes in OLEDs, indicating these complexes are electron trapping instead of hole trapping. Long-lived phosphorescent OLEDs fabricated with these new Ir complexes give external quantum and power efficiencies above 18% and 33 lm/W, respectively.

10.1: Broadband-Emitting Microcavity-OLED Device

We demonstrate a broadband-emitting microcavity-OLED device by applying a light-scattering layer to a microcavity device to integrate its angular-dependent narrow-band emission and to detrap shorter wavelength light from the substrate. The luminous efficiency is improved, and the use of a thin metal film, in place of ITO, permits larger feature sizes and reduces device costs.