Thin film devices made with poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene], MEH‐PPV, are known to be efficient light‐emitting diodes. The same devices, under reverse bias, exhibit excellent sensitivity as photodiodes. Thus the polymer tunnel diode is a dual‐function device. For the Ca/MEH‐PPV/ITO (indium/tin oxide) layered structure, the external quantum efficiency for electroluminescence is ≊1% photons/electron (forward bias ≳2.5 V). The same device is sensitive as a photodiode: The dc sensitivity (−10 V, reverse bias) is 9×10−2 A/W (at ∼1‐μW/cm2 input) corresponding to a quantum yield of more than 20% electrons/photon.