Evaluation of Solar Cells by Means of Spectral Analysis

The solar cell is a device which converts light energy into electrical energy. The electrical output of the cell, or response, depends on the spectral composition of the incident light. For space applications, determination of the response of solar cells to sunlight not filtered by the atmosphere is of great importance. In characterization of the performance of a solar cell under outer space illumination, the most important parameter is the short-circuit current under such illumination. Once this current is known, the current-voltage output characteristic can be measured under a light source of arbitrary spectral distribution but of an intensity adjusted to produce the outer space short-circuit current. This paper shows that it is practical to obtain the outer space shortcircuit current from measurements of the spectral response of solar cells. Of the alternative approaches, one method relies on measurements under terrestrial sunlight while another method attempts to simulate the spectrum of the sun. Each of these two methods has practical difficulties that offset its inherent simplicity. The direct sunlight measurements must be made outdoors unless * Sandia Corporation, Albuquerque, New Mexico. 1103