Nanostructured iodine films with control the thickness which from 0- to 100- sweep-segments successfully electrodeposited on PEDOT/ITO glass substrates using the cyclic voltammetry (CV) method at room temperature. The formation mechanism of the iodine-PEDOT film is monitored by CV techniques, UV-visible spectroscopy, alternating current (AC) impedance spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). CV and AC impedance spectroscopy reveal that the iodine-PEDOT CEs have higher electrocatalytic activity for the I3−/I− redox reaction and a smaller charge transfer resistance than the PEDOT electrodes. It is found that iodine-PEDOT increased the reactive interface, which supports charge transfer at the interface. With an optimum iodine film thickness of 50 sweep-segments on PEODT CEs, a 19.5% improvement in the cell efficiency (from 4.1 to 19.5%) is achieved.