Lifetime limitations of epitaxial P and N-type Si foils

In this publication we present p- and n-type Si foils with thicknesses between 40 and 150 μm produced with epitaxy on porous Si followed by mechanical lift-off. We discuss the influence of thickness and surface passivation quality on the relation between τ_eff and τ_bulk. Appearing inhomogeneity of minority carrier lifetimes over the sample area is found to be due to porous Si removal and surface cleaning issues. However, on n-type Si foils we could achieve τ_bulk values of up to 800 μs. As such Si foils are sufficient for conversion efficiencies well above 20% [1] we are confident that solar cells can be processed with our material exceeding this benchmark.