Conversion of Solar to Electrical Energy

Abstract

A photovoltaic device has been developed which converts solar radiation directly into electrical energy with an over-all efficiency of 11%. This consists of a p-n junction formed by gaseous diffusion near the front surface of a silicon plate. In full sunlight a single cell furnishes approximately 30 ma of short circuit current per square centimeter of surface, 0.6 v of open circuit voltage, and 12 mw of power into a matched load per square centimeter of surface. Like other electric batteries, individual cells may be connected in series or parallel to obtain an increase in terminal voltage or current. The spectral response is a maximum near 0.7 µ, and the long wavelength cutoff is at approximately 1.1 µ. The efficiency of this new silicon p-n junction photovoltaic cell is greater by a factor of 20 than that previously reported for other types of photocells and makes the conversion of the sun's energy directly into electricity possible for a number of interesting applications. A Bell System field trial at Americus, Georgia, in which solar batteries are used to power a rural carrier telephone communication system, is described. A number of other possible applications for this new solar energy converter are discussed.