Low-reflective transparent conducting films of indium oxide by vacuum evaporation and their application to amorphous silicon solar cells

Transparent conducting films of metaloxides essentially show high reflection over 10%, which often prevents them from being utilized as a transparent heater, an infrared reflector, etc., in optical devices. This report describes a vacuum-evaporating method of low-reflective transparent conducting films of indium oxide and their application to amorphous silicon solar cells as transparent electrodes. Indium-oxide films doped with 3 wt % tin-oxide were evaporated at an oxygen pressure of 0.0003 Torr on so slide-glass plates heated at a temperature of 400C. The film's average reflectance in the visible region decreased gradually with increasing deposition rate, and lowered down to a level of a bare substrate glass surface at a deposition rate of 7 A/s. Such low reflections of the films seemed to be due to optical inhomogeneities that occurred from rough grain structures in their upper layers. The similar reduced reflections appeared also on the front faces of amorphous silicon solar cells which use these inhomogenous indium-oxide films as transparent electrodes. As a result, the amorphous silicon solar cells with properly inhomogeneous indium-oxide film's electrodes exhibited fairly enhanced photovoltaic conversion efficiencies in comparison with that with homogeneous ones.