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Zhang J.,Shanghai University of Electric Power | Liu C.,Xian University of Science and Technology | Cheng G.,Shanghai Tianyi Electrical CO. | Chen X.,Shanghai Tianyi Electrical CO. | And 3 more authors.
Journal of Information Display | Year: 2014

It is currently hard to estimate the reliability parameters of organic light-emitting diodes (OLEDs) when conducting a life test at normal stress, due to the remarkably improved life of OLEDs to thousands hours. This work adopted three constant-stress accelerated life tests (CSALTs) to predict the life of white OLEDs in a short time. The Weibull function was applied to describe the life distribution, and the shape and scale parameters were estimated using the least square method. The experimental test data were statistically analyzed using a self-developed software. The life of white OLEDs predicted via this software is in good agreement with that reported from the customers. The numerical results indicated that the assumptions of CSALT are correct, and that CSALT can be used to predict the life of white OLEDs. This work confirmed that the life of white OLEDs meets the Weibull distribution, and that the accelerated life equation conforms to the inverse power law. Furthermore, the precise accelerated parameters were shown to be particularly useful in enabling the rapid estimation of white OLEDs' life. © 2014 © 2014 The Korean Information Display Society. Source


Zhang J.P.,Shanghai University of Electric Power | Liu C.,Xian Jiaotong University | Chen X.,Shanghai Tianyi Electrical CO. | Cheng G.L.,Shanghai Tianyi Electrical CO. | Zhou A.X.,University of North Carolina at Charlotte
Luminescence | Year: 2014

In order to obtain reliability information for a white organic light-emitting diode (OLED), two constant and one step stress tests were conducted with its working current increased. The Weibull function was applied to describe the OLED life distribution, and the maximum likelihood estimation (MLE) and its iterative flow chart were used to calculate shape and scale parameters. Furthermore, the accelerated life equation was determined using the least squares method, a Kolmogorov-Smirnov test was performed to assess if the white OLED life follows a Weibull distribution, and self-developed software was used to predict the average and the median lifetimes of the OLED. The numerical results indicate that white OLED life conforms to a Weibull distribution, and that the accelerated life equation completely satisfies the inverse power law. The estimated life of a white OLED may provide significant guidelines for its manufacturers and customers. © 2014 John Wiley & Sons, Ltd. Source


Zhang J.,Shanghai University of Electric Power | Li W.,Shanghai University of Electric Power | Cheng G.,Shanghai Tianyi Electrical CO. | Chen X.,Shanghai Tianyi Electrical CO. | And 2 more authors.
Journal of Luminescence | Year: 2014

In order to acquire the life information of organic light emitting diode (OLED), three groups of constant stress accelerated degradation tests are performed to obtain the luminance decaying data of samples under the condition that the luminance and the current are respectively selected as the indicator of performance degradation and the test stress. Weibull function is applied to describe the relationship between luminance decaying and time, least square method (LSM) is employed to calculate the shape parameter and scale parameter, and the life prediction of OLED is achieved. The numerical results indicate that the accelerated degradation test and the luminance decaying model reveal the luminance decaying law of OLED. The luminance decaying formula fits the test data very well, and the average error of fitting value compared with the test data is small. Furthermore, the accuracy of the OLED life predicted by luminance decaying model is high, which enable rapid estimation of OLED life and provide significant guidelines to help engineers make decisions in design and manufacturing strategy from the aspect of reliability life. © 2014 Elsevier B.V. Source


Zhang J.,Shanghai University of Electric Power | Chen W.,Shanghai University of Electric Power | Wang C.,Shanghai University of Electric Power | Chen X.,Shanghai Tianyi Electrical CO. | And 3 more authors.
Microelectronics Reliability | Year: 2015

Aiming at precisely predicting the life of the high-power white light LED (HPWLED), a three-parameter Weibull function and the right approximation method were employed to establish the luminance degradation model. The lumen maintenance data collected according to the IES LM-80-08 lumen maintenance test standard were fitted with and without error corrections, and the pseudo failure time of each HPWLED sample was extrapolated. The statistical analysis on the failure time was achieved by using Weibull distribution, normal distribution, lognormal distribution and Akaike Information Criterion (AIC). Then the life information was acquired. The results indicate that Weibull right approximation luminance degradation model (WRALDM) accurately reflects the variation of the lumen law with time. The failure time is accurately obtained. The best life distributions before and after the error correction to the lumen maintenance data are identified, based on AIC, as Weibull distribution and lognormal distribution, respectively. It is further confirmed by comparing the widths of life confidence interval and the life provided by the IES TM-21-11 method that the HPWLED life using WRALDM has a better accuracy. The optimized model provides researchers and manufacturers with significant guidelines for the further development of life prediction methodology. © 2015 Elsevier Ltd. Source


Zhang J.P.,Shanghai University of Electric Power | Wang C.,Shanghai University of Electric Power | Chen X.,Shanghai Tianyi Electrical CO. | Cheng G.L.,Shanghai Tianyi Electrical CO. | And 2 more authors.
Luminescence | Year: 2015

In order to accurately acquire the life time information for the organic light emitting diode (OLED), an experiment based on the normal stress life test was carried out to gain the data for the luminance degradation tests. The luminance degradation model of OLED was established based on the Weibull function and the least square method. Combined with luminance degradation data, Weibull parameters were estimated, the qualitative and the quantitative relationship between the initial luminance and the OLED life was obtained, and the life estimation of the product was achieved. Numerical results show that the test scheme is feasible, the luminance degradation model proves to be reliable for the OLED life estimation, and the fitting accuracy is very high by comparison with the test data fluctuation. Moreover, the real life time of the OLED is measured, which can verify the validity of the assumptions used in accelerated life test methods and provide manufacturers and customers with significant guidelines. Copyright © 2014 John Wiley & Sons, Ltd. Copyright © 2014 John Wiley & Sons, Ltd. Source

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