Surface Effects in Silicon Solar Cells

Very low-energy protons (0.4 to 27.5 kev) were used to study surface effects in silicon solar cells. The types of solar cells tested included conventional cells of n/p and p/n construction, as well as recently developed lithium-doped p/n cells (supplied by Heliotek Inc.). A proton beam of selected energy was used as a probe to penetrate to specified depths within the cells. Characteristic V-I curves were obtained before, during, and after proton exposure. Proton-induced degradation of the cell characteristics were analyzed. Anomalous damage, including partially recoverable losses of open-circuit voltage and significant losses of maximum power, were identified with various regions of the cells by correlation with proton penetration depths.