In this work, we use microwave exposure of tungsten and molybdenum oxides to improve hole extraction in organic photovoltaics (OPVs). This is a result of fast recovery of the high work function of metal oxides occurring within a few seconds of microwave processing. Using the space-charge-limited current model, we verified the formation of an anode contact that facilitates hole extraction, while Mott-Schottky analysis revealed the enhancement of the device built-in field in the devices with the microwave-exposed metal oxides. Both were attributed to the formation of large interfacial dipoles at the ITO/microwave-exposed metal oxide interface. The power conversion efficiency (PCE) of OPVs using microwave-exposed metal oxides and based on blends of poly[(9-(1-octylnonyl)-9H-carbazole-2,7-diyl)-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) with ([6,6]-phenyl-C71 butyric acid methyl ester, PC71BM) reached values of 7.2%, which represents an increase of about 30% compared with the efficiency of 5.7% of devices using metal oxides not subjected to microwave exposure.
Keywords: charge transport; interfacial dipole; microwave exposure; organic photovoltaics; transition-metal oxides.