A degradation model for blue fluorescent OLEDs for compensation of decreased pixel luminance and lifetime enhancement of OLED displays

• Applicant: Professor Dr.-Ing. Chihao Xu
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Image and Language Processing, Computer Graphics and Visualisation, Human Computer Interaction, Ubiquitous and Wearable Computing
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282450530

The aim of an OLED degradation model is to determine the efficiency of an OLED during the lifetime of an OLED display. This enables the compensation of the differential aging of the pixels and the suppression of the biggest problem of an OLED display, image sticking.In the previous project, a correlation model and a data counting model for the OLED degradation were developed. The correlation model correlates the measurable current drift with the drift of the efficiency, while the data counting model calculates the decreased efficiency from the accumulated stresses of the OLED pixel. The efficiency obtained from the correlation model and/or the data counting model is stored as the aging state and used for the next level of the degradation model, the electro-optical model. In this way, the efficiency in dependence on the aging state and the operating point can be simulated.The goal of this new project application is to suppress the image sticking artifact with a real-time compensation algorithm based on this novel electro-optic model. This should make the model applicable.In the first phase of the new project, the strengths of the correlation model and the data counting model will be combined. A specific algorithm is to be derived which, based on the electro-optical model, determines the efficiency as a function of the aging state and the operating point. The fact may be beneficial that the aging state for the real time operation can be considered as constant.Digital driving of AMOLEDs has some advantages particularly for the aging compensation. The operating point lies in a relatively narrow range with little color shift. The higher gray scale resolution necessary for the compensation can be easily and accurately realized with time-based digital driving. The image decomposition for digital AMOLEDs, however, requires some complexity. The image decomposition and the aging compensation form an interdependent system, so that special attention must be paid to the efficiency of the algorithm. An integrated method for image decomposition and aging compensation will be designed and developed in such a way that the logic complexity will increase just moderately.The value of the degradation model lies mainly in the suppression of the image sticking artifact, which can only be confirmed and evaluated by HW validation. The algorithm is implemented in an FPGA and is intended to drive a digital AMOLED prototype of medium size and high resolution specifically designed by us for that purpose. By performing a user test, the effectiveness of the aging compensation can be evaluated and the lifetime enhancement of OLED displays can be quantified. Finally, the potential challenges of aging compensation for analog driving are to be identified.

• DFG Programme: Research Grants