Multi-layer deposition of conformal, transparent, conducting oxide films for device applications

Abstract

Conformal, high conductivity thin films of indium tin oxide (ITO) have been deposited utilizing a relatively low temperature, ambient, multi-layer dip coating process. Using standard alcohol solutions of indium chloride and stannic chloride to form ultra-thin layers, consecutive multi-layer deposition of ITO onto telecommunications grade glass fibers (as a model system) showed excellent control over grain morphology in the film as determined by electron microscopy, and a linear relationship between thickness and overall fiber conductivity. Ray tracing coupled with a transfer matrix formalism was used to numerically simulate the effects of film thickness on the optical waveguiding nature of the conducting layer. The simulations, carried out for a generic film morphology, show that a significant fraction of the optical energy coupled into the fiber face, is transmitted into the film at the thicknesses studied. These results were then used to estimate an upper limit of optical power transmission provided for the generic system. From this a comparison between the optical performance of sputter deposited and multi-layer conducting oxide films in a device configuration could be made. Organic photovoltaic devices, using both sputter deposited and multi-layer conductors on optical grade fibers, were fabricated and tested. Both compared favorably to the numerical simulations, suggesting that the overall, long range performance between the multi-layer deposited and sputtered films are comparable as cathodes for such conformal devices.