Measurement of bulk and rear recombination components and application to solar cells with an Al back layer

A procedure to discriminate the recombination in the bulk and highly doped layers is presented in this paper. It is based on the photoconductance decay technique. First the effective lifetime is measured for the whole sample, and then the recombinant surfaces are chemically etched and the bulk lifetime is measured by itself. This method has been applied to determine the recombination associated to Al diffusion in silicon wafers after several drive-in processes. Best values are 2000 cm/s on 1.6 Ω cm p-type wafers, obtained after driving 3 μm Al at 1050 °C for 3 h in a conventional furnace. After some processes they have also been measured effective recombination velocities over 10,000 cm/s. An insufficient BSF effect cannot explain such high values in those cases, and other questions like an insufficient gettering of impurities must be considered.