We present an approach to estimating the light-trapping of thin film silicon solar cells by comparing the measured
quantum efficiency spectrum and the theoretical absorptance spectrum based on ideal diffractive light scattering. The
ideal diffractive absorptance enhancement is about 50 in silicon-based cells. We have surveyed published results for
many nanocrystalline silicon cells; the largest empirical enhancement is about 25. We discuss the physical mechanisms
leading to the reduced quantum efficiencies.