The internal luminescence quantum efficiency is one limiting factor for the performance of organic light-emitting diodes. Photoluminescence measurements are frequently used to estimate but these neglect effects of the local environment of the emissive sites and the electrical excitation mechanism. We present a method for the in situ measurement of under electrical operation. The current efficiency of several devices with different emitter-cathode distances is quantitatively compared. Precise optical simulation allows determining without additional assumptions.
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