PHOTORESPONSE OF UNDOPED AND IODINE-DOPED IRON-OXIDE THIN-FILM ELECTRODES

Undoped and iodine doped iron oxide thin films were prepared spray pyr olytically and their photoresponse towards the water splitting reactio n in alkaline medium (pH 13) was studied. The optimum spray time and t he corresponding film thickness for maximum photoresponse were determi ned. An undoped iron oxide film approximately 50 nm thick gave rise to a maximum photocurrent density and its wavelength-dependent absorptio n coefficients of light were also measured. Raman spectroscopic analys is indicates the formation of alpha-Fe2O3 film by the spray pyrolytic method. The band gap of this undoped film was found to be 1.97 eV. A t heoretical expression of photocurrent density at the thin film electro de-solution interface was developed. A good correlation was found betw een theoretical and experimental photocurrent densities. Importantly, such an iodine-doped iron oxide film approximately 100 nm thick gave r ise to a fivefold increase in maximum photocurrent density compared wi th an undoped optimum thick film of approximately 50 nm. These observa tions were attributed to increased mobility of carriers and an increas e in the absorption of light in the iodine-doped film. Model calculati ons show that five undoped iron oxide thin film electrodes of optimum thickness in stacks generate a photocurrent density of 5 mA cm-2 where as an optimized stack of iodine-doped film produced a photocurrent den sity of 15 mA cm-2 at 0.82 V vs. SHE.