A lithographic fabrication method for a new interdigitated array microelectrode (IDA) consisting of optically transparent (ITO) and nontransparent (Pt) arrays of band electrodes on a quartz substrate is presented. The new IDA is applied to the Ru(bpy)(3)(2+)-Fe3+ photogalvanic system. The effective separation of photoinduced active species between Very closely spaced electrodes is achieved by utilizing the shadow of the nontransparent electrode generated by illumination from the rear of the IDA. This back-illumination method using the new IDA is effective in increasing the conversion efficiency.