The preparation and properties of ITO/tin/silicon solar cells
Transparent semiconducting oxide films of ITO have been deposited using screen printing techniques for fabricating heterostructure solar cells. The ITO material used is a readymade combination of organometallic compounds of indium and tin, dissolved in a suitable organic vehicle to make a screenprintable ink or paste. The paste is then printed onto substrates in the desired configurations. The effect of various firing temperatures, from 450°C to 650 °c, on the film properties were observed. The sheet resistances, Ra, changed as the firing temperature varied. Ra values could be decreased by annealing the films in an inert gas or in vacuum conditions. An annealing temperature of 300°C seemed to be optimum for annealing the ITO films. This decreased the sheet resistance by a factor of more than ten. The lowest sheet resistance of the ITO films was about 290 n/sq, measured during annealing under vacuum conditions at a temperature of 300 °C. This gradually increased up to about 1 Kn/sq after the film was aged for a few days in a laboratory atmosphere. The solar cell structures of ITO/p-Si and ITO/Sn/p-Si were made in this research. The first structure suffered from an excessive oxide interfacial layer thickness and it was abandoned. The second structure was then made to overcome the problems resulting from the interfacial oxide. The Sn layer was produced by using evaporation prior to the screen printing of ITO. The thickness of the Sn layer was about 100 nm. After evaporation, screen printing methods were used to complete the heterostructure solar cell. The best typical values of these cells are, open circuit voltage, V~= 0.360 Volt, short circuit current density, Jsc= 16.4 mA/cm2 with fill factor, FF = 0.34 and efficiency, 1) = 2.5% under 80 mW/cm2 simulated illumination, where this illumination is equivalent to air mass 2, (AM2).