Separating photocurrent and injected current contributions to the organic magnetoresistance

The magnetoresistance in the photocurrent and injected current of an organic device has been studied. When such a device is illuminated under bias, both photo-generated charges and electrically injected carriers will contribute to the current. We used a magnetic field modulation to successfully remove the time-dependent change in the current. This was combined with a modulation of the intensity of the illumination to separately measure the effects of the photocurrent. At low bias, without illumination no magnetoconductance (MC) is observed in leakage current, while with illumination an MC is observed due to the photo-generated charges. With increasing voltage, as electrical charge injection starts, the width of the MC curves as a function of magnetic field of the photocurrent remains constant and is larger than the curve observed for the electrically injected current, even when both currents are present. This result shows that the contributions from the photocurrent and the injected current cannot be combined, but should be treated separately.