This paper describes a novel optical measurement technique for the in situ determination of the spatial temperature distribution at the organic layer level in large-area organic light-emitting diodes (OLEDs). The local junction temperature of OLEDs is a very important factor with respect to the luminance uniformity. Moreover the variation of local temperatures leads to a non-uniform depreciation of its light output, which in turn increases the luminance non-uniformity over time and affects the lifetime expectancy of the OLED.
Junction temperature maps can be derived from easily measurable luminance maps after a dedicated calibration procedure. The underlying model based on the relationship between the local diode electrical behavior and the light emission at different temperatures. The method is illustrated for the self-heating of a commercially available OLED for lighting, and validated by comparison with infrared thermography.