The potential profiles along the channel of Al/Poly(3-hexylthiophene), PHT film/Au diode from Al to Au electrodes have been measured directly using nanomanipulator with potential probing tips. The steep potential cliff is observed at the interface of Al/PHT, indicating the existence of depletion layer with higher resistance than that of bulk region. For the forward bias, the resistance at the depletion layer decreased significantly and the potential gradient in the PHT bulk region is observed above the onset bias of 1 V. It is found that the contact resistance of PHT/Au is unexpectedly large in spite of the ohmic behavior and also for Al/PHT at forward bias. The effect of light on the depletion layer will be also mentioned. It is stressed that the contact resistances of PHT and metals are significantly important to improve the performance of organic electronics devices.
