Study of solar power conversion using electrochemical photovoltaic semiconducting n-CdSe0.7Te0.3 thin film ferro-ferricyanide electrolyte junction

Abstract

Polycrystalline thin films of semiconducting n-CdSe0.7Te0.3 of thickness approximate to 5000 Angstrom were deposited in a vacuum of 5 x 10(-5) torr by thermal flash evap oration of the powdered bulk alloy at a deposition rate of 20 +/- 1 Angstrom/sec on highly conducting In2O3 precoated (sigma = 125 x 10(2) (Omega cm)(-1)) microslide glass plates held at 200 degrees C. The films when characterized by XRD were found to have a hexagonal structure. Optical absorption studies showed the band gap to be direct (approximate to 1.56 eV). Three electrode configuration of electrochemical photovoltaic (ECPV) solar cell comprising of saturated calomel electrode (SCE), graphite and n-CdSe0.7Te0.3 semiconducting thin film photoanode was used. The ECPV solar cell was illuminated by Tungsten filament - Iodine lamp at 100 mW/cm(2) AM1.5 illumination intensity. The as-grown films were found to be photoactive in conjunction with (aq) 0.1 M KI Fe(CN)(6) + (aq) 0.3 M Ks Fe(CN)(6) + (aq) 0.3 KOH redox electrolyte. A 4 cm(2) area of the exposed thin film photoanode in the PEC cell yielded a power conversion efficiency of about 2.74 %. This high efficiency of the as-fabricated PEC solar cell using as-deposited CdSe0.7Te0.3 thin film is due to the high value of the flat band potential (approximate to -850 mV vs SCE) which was measured from Mott-Schottky plots at 1 kHz and gave a high equilibrium band bending of approximate to 960 meV. These results indicate that for other redox electrolytes used in the ECPV solar cells like (aq) polyiodide, (aq) polysulphide, etc the band bending is not so high. Secondly, the larger positive redox potential of this ferro-ferricyanide system (approximate to 150 mV SCE) leads to larger bending of bands. Also, photocorrosion inhibition is strong, leading to higher stability of the solar cell.