A simple method for the photometric characterization of organic light-emitting diodes (OLEDs) is reported. It is based on the indirect measurement of the total emitted optical power by using a calibrated photodiode and the optical emission spectrum and space emission diagram of the OLED. From this and by measuring the current-voltage characteristic of the OLED all the relevant radiometric and photometric quantities can be extracted, including the external quantum efficiency. The usual method to collect all photons emitted by a LED source in the half space uses an integrating sphere with the LED source placed at the entrance hole and a photodiode (PD) placed at an exit hole at some point on the sphere surface. Here we show that the same result can be also achieved in free space by a simple geometrical arrangement of the PD in respect of the OLED source, with no need of an integrating sphere. Moreover, we find that a large area photodiode placed in contact with the OLED surface measure about 82% of the total emitted power.
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