The short-circuit current decay technique has been used in the literature to determine the minority-carrier lifetime in the base of solar cells. The dependence of the short-circuit current decay on the wavelength of the excitation light is reported in detail. Both the theoretical expressions and experimental results are presented. The experimental results agree reasonably well with the theory.
An expression for the forward current induced open circuit voltage decay of a p-n junction diode with a finite base width is derived. The expression includes the effects of recombination in the emitter and the built-in drift field in the base which may arise due to a nonuniform impurity profile. The voltage decay rate is dependent on the base thickness, base drift field, emitter dark saturation current, the effective surface recombination velocity at the back contact, and the minority carrier lifetime in the base. The effects of the drift field in the emitter, emitter lifetime, and surface recombination velocity at the emitter surface are completely taken into account by the emitter saturation current. Experimentally observed voltage decay plots for thin base hyperabrupt varactor diodes with retrograded impurity gradients in the base are reported. It is shown that the experimental results can be interpreted satisfactorily using the above theory. The values of the minority-carrier lifetime in the base are determined from the experimental results.
The expressions for the open circuit photovoltage decay in a p-n junction solar cell are derived, including the effects of recombinations in the emitter. It is shown that for a cell with base thickness wB≫LB, the base diffusion length, the voltage decay rate for small values of time depends on the emitter dark saturation current JE0; the larger the value of JE0 , the faster is the initial rate of voltage decay. For large values of time, the rate of voltage decay is solely determined by the minority carrier lifetime in the base τB and is independent of JE0 . However, for a cell with wB≲LB, the voltage decay is linear from the very beginning and the decay rate is of the form (kT/e)[(1/τB) +(1/t1)]. The time constant t1 is independent of τB . It, however, depends on the base thickness, the effective back surface recombination velocity, and the emitter dark saturation current JE0 . The value of JE0 depends on emitter thickness, front surface recombination velocity, drift field in the emitter, band-gap narrowing, and Auger recombinations in the emitter.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.