Field emission from carbon-nanotube-dispersed conducting polymer thin film and its application to photovoltaic devices

We investigated the field emission properties of single-wall carbon-nanotube (CNT)-dispersed conducting polymer thin film prepared by spin coating and electrophoresis. A p-type conducting polymer such as poly(3-octylthiophene) (P3OT) or poly(2-methoxy, 5-(2'-ethyl-hexyloxy)-p-phenylenevinylene) (MEHPPV) doped with CNTs is an excellent field emitter. The field emission was successfully reproduced by an electrophoretic technique and the turn-on fields of CNT-dispersed P30T films were 4-6V/mu m. Moreover, the field emission properties were markedly improved by post-field treatment on a thermally oxidized Si wafer, and a low turn-on field of 1.6V/mu m was successfully obtained probably due to the improved vertical orientation of CNTs. New devices having both photovoltaic and field emission properties were also demonstrated. We also investigated the photovoltaic properties of the devices composed of ITO/TiO(2)/CNT-MEHPPV composite/Au structure. The open-circuit voltage V(OC) and short-circuit current density I(SC) of. the device without CNTs were 0.6V and 0.4mA/cm(2), respectively, under 100mW/cm(2) white light illumination. Although V(OC) and I(SC) were not considerably improved, a marked increase in current density, more than a factor of 1000 at - 1V, was obtained for the device with a CNT-dispersed MEH-PPV layer. Such an increase in current density was obtained only in negative biasing on the Au top electrode and we attributed this increase to the field emission of electrons from CNTs into the Ti0(2) layer.