Effect of wet-chemical substrate pretreatment on electronic interface properties and recombination losses of a -Si:H/c -Si and a -SiN_x:H/c -Si hetero-interfaces

Surface charge, surface state density and interface recombination behavior on polished float zone (FZ) solar cell substrates were investigated after various wet-chemical pre-cleaning procedures and deposition of amorphous silicon (a-Si:H) or silicon nitride (a-SiNx:H). Applying surface photo voltage (SPV), microwave detected photo conductance decay (µW-PCD) and transient microwave conduction (TRMC) measurements, electronic interface properties were monitored repeatedly during the preparation processes. As shown for an inverted a-Si:H/c-Si hetero-junction structure, with front side passivation by a-SiN_x:H and a p-type a-Si:H emitter on the rear side, the effect of optimised wet-chemical pre-treatment can be preserved during the subsequent soft plasma enhanced chemical vapour deposition of a-Si:H or a-SiN_x:H. This leads to hetero-interfaces with low interface recombination velocities. These results were compared to previously reported findings, obtained on textured Czochralski (CZ) single crystalline substrates. a-SiN_x:H is known to result in a field effect passivation. Nevertheless a strong influence of wet-chemical treatments on surface charge and recombination losses was observed on both flat and textured a-SiN_x:H/c-Si interfaces. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)