To minimize interfacial power losses, thin (5–80 nm) layers of NiO,
a p-type oxide semiconductor, are inserted between the active
organic layer, poly(3-hexylthiophene) (P3HT) [6,6]-phenyl-C61
butyric acid methyl ester (PCBM), and the ITO (tin-doped indium
oxide) anode of bulk-heterojunction ITO/P3HT:PCBM/LiF/Al solar
cells. The interfacial NiO layer is deposited by pulsed laser deposition
directly onto cleaned ITO, and the active layer is subsequently
deposited by spin-coating. Insertion of the NiO layer
affords cell power conversion efficiencies as high as 5.2% and
enhances the fill factor to 69% and the open-circuit voltage (Voc)
to 638 mV versus an ITO/P3HT:PCBM/LiF/Al control device. The
value of such hole-transporting/electron-blocking interfacial layers
is clearly demonstrated and should be applicable to other organic
photovoltaics.