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 τeff and τbulk. 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 ntype Si foils we could achieve τbulk 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.