Optimization of transparent electrode for solar cell and chemical vapor deposition of amorphous silicon. Final technical report, 15 September 1980-30 March 1983

Abstract

A film of fluorine-doped tin oxide can meet all these requirements. A new process for depositing fluorine-doped tin oxide films was optimized. Further optimization of the transparent electrode films has been accomplished, with increasing substrate temperature being identified as a primary variable for obtaining better films. Deposition conditions for obtaining either smooth or rough films were identified, and the surface morphology was characterized by SEM photographs and by measurements of diffuse light scattering. Film growth rates were determined as a function of reactant concentrations. We developed a simple, sensitive and reliable method for measuring the interfacial or contact resistance between tin oxide and silicon. When this method was used to measure the contact resistance between highly conductive tin oxide films and highly doped silicon, values often exceeded 10 ..cap omega..-cm/sup 2/. Next, structures were tested, which incorporate a layer of highly doped, electrically conductive titanium oxide between the tin oxide and the silicon. These structures showed much lower contact resistances. Thermal degradation of these contacts was not found even at temperatures as high as 600/sup 0/C. Amorphous silicon films were prepared by chemical vapor deposition. Electrical and optical properties were found to be similar to those of amorphous silicon producedmore » by glow discharge. Hydrogen content of the films was typically 8 to 10%, and did not vary significantly with substrate temperature. The optical band gaps of the CVD material were slightly smaller than glow discharge a-Si of the same hydrogen content. Doping the CVD films during growth with boron or phosphorous produces conductivities on the order of 300 ..cap omega..-cm. Schottky diode cells with a structure stainless steel/n-Si/i-Si/Pt show an efficiency of about 3%, after correction for the transmission of the platinum layer.« less