Electrical short-circuit current decay: Practical utility and variations of the method

Abstract

We review and extend the theory and experimental practice of the electrical short-circuit current decay (ESCCD) method for determining the effective back surface recombination velocity S and minority-carrier lifetime τ in p-n junction solar cells and diodes. The ratio of minority-carrier diffusion length to base thickness plays a key role in the transient ESCCD response which in general is an infinite sum of decaying exponentials. Their amplitudes and decay constants depend on this ratio. If this ratio is much less than unity, the response decays in proportion to (t/τ)−3/2 exp(−t/τ) for times that can be explored experimentally. If this ratio exceeds unity, a single mode of exponential decay predominates. For all intermediate cases a multimode fitting procedure yields S and τ. We present, with illustrative measurements of solar cells, three different ways to improve accuracy of the ESCCD method: (a) observing the amplitude and the decay constant for different injection levels, (b) altering the device under study by replacing the low-high junction (or back-surface-field region) by an ohmic contact, and (c) combining the observed decay constant with results of low- or high-frequency small-signal-admittance measurements.