Metal oxide coated p–n junction silicon electrodes for photoelectrochemical solar energy conversion

Photoelectrochemical properties of p + –n junction silicon electrodes, abbreviated as p + n–Si, coated with thin oxide films of titanium, tungsten, or iron have been investigated in aqueous solutions of hydrogen iodide and iodine. The films were deposited by electron-beam evaporation of the metal oxide sinters. The photocurrent in a p + n–Si electrode coated with TiO 2 increased dramatically when it was heated at temperatures higher than 500 °C, though the O/Ti atomic ratio as determined by ESCA analysis was unchanged. The fill factor of the photovoltaic cell composed of this electrode, a platinum counter electrode and an aqueous solution of 7.6 M HI and 0.03 M I 2 was improved by coating with ruthenium or its oxide. The photovoltaic cell attained a high solar to electrical energy conversion efficiency of 9.3% (AM1), with an open circuit photovoltage of 0.58 V, a short circuit photocurrent of 26.6 mA cm −2 and a fill factor of 0.61. The photocurrent was stable for 350 h. For the cases of electrodes coated with a Fc 2 O 3 or WO 3 film, high fill factors were obtained even without ruthenium coating. The effect of the nature of Si – metal oxide junctions, the donor density in the oxide, the relations between the flat band potential of the oxide and the redox potential of the solution, etc., on the conversion efficiency was discussed.