Photoresponse of poly(para-phenylenevinylene) light-emitting diodes

We have studied the photoresponses of poly(para-phenylene vinylene) (PPV) light-emitting diodes (LED’s) with PPV derivatives sandwiched between tin oxide (ITO) and metals including calcium, aluminum, and copper. Under illumination all diodes exhibit relatively large photoconductive I(V) responses which cross the dark I(V) curve at a forward-bias voltage ${\mathrm{V}}_0$ that scales with the difference in work functions between the ITO and metal electrodes, the open-circuit voltage saturates at ${\mathrm{V}}_0$ and is temperature independent, and the enhanced electroluminescence intensity of the illuminated LED’s correlates with the photocurrent. (AIP)