Performing quasi-steady-state lifetime measurements using two different illuminating spectra provides quantitative information about bulk lifetime (tau(b)) and surface recombination velocity (S). This paper motivates the investigation of this relatively new method by demonstrating that the conventional method of iodine/methanol passivation for the extraction of tau(b). which is then used to calculate S for a dielectric, may fail for solar-grade materials such as string ribbon silicon. To facilitate the use of the two-spectrum method, first we introduce a novel empirical procedure for the determination of the constant of proportionality between the short-circuit current of the reference cell and the average generation rate (G(av)) in the test wafer. Then a sensitivity analysis is performed to show that the method of using a white light spectrum and an infrared spectrum to obtain information about tau(b) and S also has serious limitations in certain cases: only a lower bound can be placed on tau(b) for tau(b) greater than about 10 mus, and only an upper bound can be placed on S for S less than about 1000 cm/s. Our analysis demonstrates that in order to use the two-spectrum method to specify tau(b) and S within a factor of about 2-20 when experimental uncertainty is +/-10%, the quality of both the bulk of the material and the surface passivation must be somewhat poor. Precision may be improved by reducing experimental uncertainty. To illustrate the requirement that bulk and surface recombination must be high in order to use the two-spectrum method with the greatest precision, the method was applied to nitride-passivated float zone and cast multicrystalline silicon wafers of different resistivity. Only an upper limit to S (165 cm/s) was inferred for the easily passivated float zone wafer, whereas both upper and lower limits to S were extracted for the less effectively passivated heat-exchanger method (HEM) multicrystalline wafers. The analysis yielded 1200 < S < 4200 cm/s for the 1.4 Omega cm HEM wafer and 3000 < S < 20000 cm/s for the 0.2 Omega cm wafer after the nitride was annealed at 850 degreesC, The 0.2 Omega cm HEM wafer was also measured before the nitride was annealed. The two-spectrum method provided a tau(b) range that remained nearly unchanged, while the S range was much higher for the as-grown SiNx This indicates that the 850 degreesC anneal improves surface passivation without passivating the bulk of the HEM material. (C) 2002 Elsevier Science Ltd. All rights reserved.