Unifying view of transient responses for determining lifetime and surface recombination velocity in silicon diodes and back-surface-field solar cells, with application to experimental short-circuit-current decay

Abstract
Two main results are presented. The first deals with a simple method that determines the minority-carrier lifetime and the effective surface recombination velocity of the quasi-neutral base of silicon solar cells. The method requires the observation of only a single transient, and is amenable to automation for in-process monitoring in manufacturing. Distinct from many other methods in use, this method, which is called short-circuit current decay, avoids distortion in the observed transient and consequent inaccuracies that arise from the presence of mobile holes and electrons stored in the p-n junction space-charge region at the initial instant of the transient. The second main result consists in a formulation of the relevant boundary-value problems that resembles that used in linear two-port network theory. This formulation enables comparisons to be made among various contending methods for measuring material parameters of p-n junction devices, and enables the option of putting the description in the time domain in the form of an infinite series, although closed-form solutions are also possible. The advantage of an infinite-series formulation is the possibility of identifying dominant relaxation times of the transient, leading thereby to simplified descriptions. By outlining the derivation of open-circuit-voltage decay and junction-current recovery from this two-port formulation, we systematically compare these methods with the short-circuit-current decay method that is emphasized here. Small-signal admittance measurement methods also emerge as special cases of the two-port formulation, as is discussed briefly.

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