Improved n-Si/oxide junctions for environmentally safe solar energy conversion

Abstract

The considerable interest in the practical use of solar energy has increased the importance of photovoltaic and photoelectrochemical systems. Metal oxide films like tin dioxide (SnO 2), titanium oxide (TiO 2) or indium tin oxide (ITO) are known to form stable photovoltaic junction with semiconductors of practical relevance like silicon (Si). Thin films of SnO 2 and TiO 2 were prepared easily and conveniently on the surface of silicon wafers by the spray pyrolysis technique. The prepared heterojunctions, i.e. the Si/oxide junction represent the main part of stable and efficient solar energy converter. In these systems, the solid/solid junction (n-Si/oxide) is separated from the site of the environmental interaction by the stable oxide film (SnO 2 or TiO 2) that protect the conventional semiconductor from photocorrosion. Besides its use in the fabrication of photovoltaic cells, the n-Si/oxide was used in the preparation of photoelectrochemical cells. The characteristics of the oxide film were subjected to a series of improvements either in the surface conductivity or the band gap energy, i.e. the position of the Fermi level of the semiconducting oxide by incorporating foreign atoms in the oxide film matrix during its preparation. The incorporation of Ru in the thin oxide film leads to the improvement of the solar conversion efficiency by improving the fill factor of the photovoltaic or photoelectrochemical cells. Such improvement enables the use of the prepared cells as clean energy converters. The fabricated solar cells have an average open-circuit potential of 0.44–0.62 V and a short circuit current of 28–30 mA/cm 2. A conversion efficiency up to 14% was achieved.