Simple hybrid current-voltage source for the characterization of organic light-emitting devices

Some organic light-emitting devices (OLEDs) behave better and longer when driven with alternating bias. It is believed that the reverse bias helps to remove the trapped charges and prevents permanent drift of ionic dopants or ion migration from electrodes. OLEDs behave much like diodes. When driven with a voltage source, the highly asymmetrical exponential I-V curve of diodes makes the accurate control of the forward current difficult. Using a voltage-controlled current source, the voltage can constantly adjust to maintain the desired current through the device. The reverse resistance of a diode is large. Using a current source to reverse bias can produce a large reverse voltage that would destroy the junction. In this article we present an electronic device used to drive and characterize organic light-emitting devices. It consists of a high voltage (+/- 225 V) hybrid source, which alternatively generates direct voltage-controlled current pulses, up to 200 mA, and reverse voltage-controlled voltage pulses. Furthermore, it allows simultaneous measurement of both, direct and reverse, current and voltage. This hybrid source, driven by an arbitrary wave form generator, makes possible the dynamical characterization of OLED when submitted to a wide variety of current and voltage signals. (c) 2006 American Institute of Physics.