Thermal behavior and indirect life test of large-area OLED lighting panels

Abstract

In this work, we studied the thermal behavior and addressed the challenges of life testing of large area OLED devices. In particular, we developed an indirect method to accurately calculate the life time of large-area OLED lighting panels without physically life-testing the panels. Using small area OLEDs with structures identical with the tested panels, we performed the life tests at desired driving current densities at different temperatures and extracted the relationship between junction temperature and the lifetime for the particular device. By measuring the panel junction temperature during operation under the same current density and using the life time measured on small area test devices, we determine the lifetime of the panels based on the thermal dependence. We test this methodology by predicting the life time of white PHOLED panels and then physically testing the panels. The typical result for the lifetime to 80% of the initial luminance (LT80) of the panel at a constant dc current density of 10 mA/cm 2 (3800 cd/m 2 ), was predicted to be 526 hours in good agreement with the actual life-test at 10 mA/cm 2 of 512 hrs. This good agreement, confirmed in different experiments, validates this novel technique as a practical life time predictor of large-area OLED lighting panels in a time saving manner.

Influence of ambient temperature on OLED lifetime and uniformity based on modified equivalent lifetime detection

“…Because OLED lifetime extension depends on several parameters, such as L 0 , n (T), compensation iterations m, L goal , and L origin , the OLED lifetime can be extended longer by optimizing these parameters according to the requirements of image quality, OLED IC driver ability, cost, OLED characteristics, and so on. There are two constraints, which is expressed in Equations (12) and (13) during the OLED lifetime extension and optimization. where L 0 , K, β, m, L goal , and L origin are same as the aforementioned.…”

“…L origin is set as 0.75 L 0 to obtain a better balance between display uniformity and lifetime extension. On the basis of two constrains of luminance compensation optimization, the compensation iterations m mainly depend on Equation (12). That means m is the same at different ambient temperature, and IC driver ability is uncorrelated to the ambient temperature.…”

“…Recently, considering thermal stress, some researches on the OLED‐aging characterization under combined thermal and electrical stresses are conducted to assess the feasibility of the detection of OLED aging, which mainly focused on junction temperature. It also has been reported that the glass transition temperature of organic layer and its low thermal conductivity will lead to degradation of devices .…”

A Novel Lighting OLED Panel Design

“…The entire device structure is as follows (Figure 1 to reduce the non-uniformity of the WOLED panel, such as using a tandem structure that can reduce the resistance of the OLED device and improve the uniformity of the WOLED panel [13], and using a different type of grid design by, say, improving the shape, width, and length of the metal mesh to improve the uniformity and emitting area of the WOLED panel [14]. The improvement of the metal mesh design can achieve good uniformity, but the OLED is a current driving device, and the metal mesh is always resistant, so the metal mesh in the emitting area of the WOLED panel always has non-negligent power dissipation and leads to reliability problems, such as the short between anode and cathode [15], and the thermal problems of the organic materials [16].…”

“…The improvement of the metal mesh design can achieve good uniformity, but the OLED is a current driving device, and the metal mesh is always resistant, so the metal mesh in the emitting area of the WOLED panel always has non-negligent power dissipation and leads to reliability problems, such as the short between anode and cathode [15], and the thermal problems of the organic materials [16].…”