Principal Investigator Vladimir Bulovic
Due to their record high absorption constant and narrow photoluminescence linewidth, thin films of J-aggregated cyanine dyes have been extensively studied with respect to their potential applications in novel opto-electronic devices, such as organic light emitting diodes, optical switches, and lasers. J aggregates’ strong absorption is especially interesting for use in light sensing devices like a photoconductor. A J-aggregate film that is only a few nanometers thick, in conjunction with a dielectric mirror, has an ability to absorb almost 100% of incoming light at normal incidence.
We demonstrate in this study an efficient lateral J-aggregate photoconductor. The device structure is a bi-layer heterojunction consisting of an optically active 5 nm thick TDBC J-aggregate thin film, which serves as the primary exciton generation layer, and a 50 nm layer of zinc indium oxide (ZIO) underneath, which serves as a charge transport layer. The contacts which sit below the ZIO are series of gold interdigitated fingers photolithographically defined on glass. The bi-layer structure physically separates the light absorption and charge transport regions of the device, taking advantage of the J aggregates’ unique optical properties and the ZIO’s charge transport properties. We observe that the heterojunction significantly increases the efficiency of the device by assisting the dissociation of the excitons, similar to earlier work. External quantum efficiency (EQE), defined as the change in number of electrons passing through the bi-layer device per incident photon. EQE greater than 100 % suggests that the exciton recombination lifetime is greater than the transit time of the electrons passing through the device. The curve follows the absorption curve of ZIO and the J aggregates shown in the inset.