Pure experimental determination of surface recombination properties with high reliability
A major task in developing new surface passivation layers for solar cells is their electrical characterization. A key value is the surface recombination velocity S. It can be extracted from the measured effective carrier lifetime tau(ind eff) in two ways: (1) with tau(ind eff) measured at one wafer and theoretical assumptions made for the bulk lifetime which leads to a major uncertainty in the S-determination. Or (2) with tau(ind eff) from a set of wafers with identically processed surfaces and different thicknesses W. Plotting ?eff in an 1/tau(ind eff) vs. 1/W-diagram, the slope of a linear fit to the data equals 2S. The infeed grinder used in our study to prepare wafers with different thicknesses is an excellent tool to produce identical, planar surfaces with low damage depth and high reproducibility. Final damage-etching gives a perfect initial point for surface texture and passivation steps. By means of this technique S is determined for oxide-passivation surfaces on different doping concentrations.