Light trapping enhancement by plasmonic-active metal nanoparticles (NPs) is believed to be a promising approach to increase silicon-based solar cell efficiency. Therefore, we investigated TiO2 films in situ doped by Au NPs (TiO2:AuNPs) deposited by spin coating on a silicon substrate. Photoconductivity and optical properties of the TiO2:AuNPs/Si structures were studied in comparison with those of TiO2/Si reference samples. We found that an introduction of the 40-50 nm diameter AuNPs into the antireflective TiO2 layer deteriorates the antireflection properties and decreases the external yield of photogeneration of charge carriers. This is due to an increase of the layer reflection in the red-IR part of the spectrum, and due to the parasitic absorption of light by AuNPs in the blue-green part. Charge carrier recombination effect at the TiO2:AuNPs/Si interface is also found to decrease the external yield. We conclude that the TiO 2:AuNPs layers could potentially be applied on the rear but not on the front side of Si solar cells. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.