In this study, the authors fabricated a transparent cathode back plate by depositing an ultra-thin film of single walled CNTs (SWCNTs) on an indium tin oxide (ITO)-coated glass substrate. First, an aqueous CNT solution was prepared by ultrasonic ally dispersing purified SWCNTs in deionized water with sodium dodecyl sulfate (SDS). After centrifugation, several milliliters or even a hundred of microliters of the well-dispersed CNT solution was deposited onto a porous alumina membrane through vacuum filtration.