In-depth characterization of silicon solar cells

An extension of the photocurrent decay (PCD) method to allow determination of the minority-carrier diffusion length in Si solar cells in a depth-resolved fashion is presented. From a single decay curve, three observables (quantum efficiency, fundamental decay time, and intercept of the extrapolated decay curve with the time-zero axis) are determined. It is demonstrated how three transport parameters, back-surface recombination velocity, the average minority-carrier diffusion length, and a third parameter which describes the depth-dependence of the diffusion length, are extracted from these observables. Computer simulations of the time-dependent minority-carrier transport problem are performed to clarify the relationships between the recombination parameters of the solar cell base and the three observables. With the experimental setup, comprising a Ti:sapphire laser, light pulses of wavelength 1010 nm are used to perform PCD measurements. Measurements on a set of polycrystalline Si cells showing that gettering treatments during cell production results in depth-dependent lifetimes were performed