Properties of indium tin oxide films prepared by the electron beam evaporation method in relation to characteristics of indium tin oxide/silicon oxide/silicon junction solar cells

Abstract

Indium tin oxide (ITO)/silicon oxide/silicon (Si) junction solar cells were produced by depositing ITO on a thin silicon oxide‐covered single‐crystal Si substrate using the electron‐beam evaporation method. The current‐voltage (I‐V) characteristics strongly depended on the incident angle (θ_i) of the evaporated ITO vapor to the Si substrate during the ITO deposition, as well as the post‐deposition heating temperature (T_h) and the kind of the ambient gases during post‐deposition heat treatment. The ITO films deposited at θ_i=0° and treated at T_h=380 °C in air formed a high‐energy barrier with p‐Si, and formed ohmic contact with n‐Si. X‐ray diffraction analysis showed that the ITO films deposited at θ_i=0° contained metal indium. The amount of the metal indium decreased either by reducing the deposition rate of the ITO film or by raising the substrate temperature during the ITO deposition. The ITO films deposited at θ_i=45° and treated at T_h=350∼450 °C in hydrogen, on the other hand, formed a high‐energy barrier with n Si. In this case, no metal indium was observed in the ITO films. It is concluded that the formation of the metal indium in the ITO films changes their work functions, and thus its presence strongly affects the I‐V characteristics of the ITO/silicon oxide/Si solar cells. Darkening observed for the ITO films deposited at θ_i=0° is also attributed to the presence of the metal indium.