Abstract
This paper describes the dependence of measuring temperature on the thin films for organic light emitting diodes (OLEDs). The final target of the present research is the improvement of flexibility of organic devices, flexible displays and flexible OLEDs. In the previous reports, the authors have demonstrated that organic thin films cause cracking as well as transparent conductive oxide (TCO) thin films in a strain of several percent at room temperature while the conductive polymer film such as PEDOT does not cause cracking. The temperature of OLED device, however, is generally heated up to less than 40ºC due to the heat generation by energy loss. Of course the temperature raise depends on the design of the device and heat sink of the panel further it influences on the life time of the device so that OLEDs cause degradation at higher temperature. Therefore, the tensile tests of Alq3, PVK, NPB, and spiro-NPB, which were prepared on PEN substrates, were conducted at a temperature of 54ºC then the critical cracking strains were compared with those measured at room temperature. As a result, it was found that the critical cracking strain of Alq3 thin films at 54ºC is higher than that at room temperature which agreed with the authors expectation, however PVK, NPB, and spiro-NPB shows lower critical cracking strain at 54ºC than at room temperature. Further study is required to understand the results from a point of the change of ductility and adhesion.
