Investigation of the double exponential in the current—Voltage characteristics of silicon solar cells

The influence of minority carrier recombination in the depletion region of silicon solar cells on their current-voltage characteristics has been investigated. Starting with cells which exhibited a clear double-exponential dark characteristic of the form with values , , and Rshlarge, depletion region recombination was studied by subjecting the cells to proton irradiation of 20- to 80-MeV energy at fluences of 10¹²to 10¹⁵cm^-2, so as to introduce further recombination centers in the depletion region. A significant change of j01resulted rather than the expected change in j02which would be caused by the introduction of deeplying levels. It could be shown that this effect, included inthe Sah, Noyce, Shockley formulation of diode current resulting from recombination in the depletion region, Was caused by the introduction of shallow levels in the depletion region by the proton irradiation. The analysis required an accurate measurement of the Characteristics over a range of temperatures and an evaluation of them with a least squares Curve fitting computer program in order to separate the effects. As a result of this study it is found that the saturation current j01is not necessarily attributable Only to diffusion current from outside the depletion region and that solely its temperature dependence can clarify its origin.