Radiation induced photocurrent in the active volume of P3HT/PCBM BHJ photodiodes

Abstract

Abstract The purpose of this work is to fabricate and characterize the response of a P3HT/PCBM bulk heterojunction organic photodiode to photon beams with respect to dose rate, total dose, and energy. A bulk heterojunction (BHJ) organic photodiode was fabricated by spin coating a blend of P3HT and PCBM onto an ITO-coated glass substrate and then depositing aluminum top contacts. Control devices were made by spin coating polystyrene instead of the P3HT/PCBM layer. The devices were irradiated with a 6 MV photon beam with dose rates of 100–600 cGy/min. Energy dependence was measured for energies of 100, 180, and 300 kVp and 6 and 10 MV. Photocurrent in the BHJ was calculated by subtracting the average current measured using the four PS devices from that measured with each of the four BHJ diodes to correct for current collected by the electrodes and the wires/connectors. The sensitivities of the four BHJ devices were within the range of 3.7–4.3 pC/cGy. The range of values is mostly due to inter-device variation and not due to variation between readings on the ITO and Al electrodes of a single device. The diodes exhibit an energy dependence with more than 4 times the response at 100 kVp than at 6 MV. The direction and magnitudes of the measured currents after correction for the electrode/lead currents were consistent with photocurrent. The photocurrents increased linearly with dose rate indicating they could be suitable in radiation sensing applications.