Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 55: Photovoltaics: Silicon-based Systems II

HL 55.1: Talk

Wednesday, March 28, 2012, 11:15–11:30, ER 270

Photo-induced tunneling current microscopy on amorphous silicon films covered by metal islands — •Andreas Englisch, Uwe Schmitt, and Uwe Hartmann — Institute of Experimental Physics, Universität des Saarlandes, P.O. Box 15 11 50, D-66041 Saarbrücken

The efficiency of thin film solar cells consisting of amorphous silicon is strongly reduced in the wavelength regime beyond 800 nm. In order to overcome this disadvantage, silver nano-particles were placed at close vicinity to the intrinsic photoactive layer. The regime of the optical resonances overlaps with the regime of low intrinsic absorbance of the amorphous silicon. The subsequent increase of the efficiency cannot be explained by optical field enhancement effects only. To understand the mechanism of charge carrier generation in the vicinity of the silver islands STM und STS-measurements were performed across an illuminated scanning area. The samples were composed of 20 nm amorphous silicon films on a 1000 nm thick ITO layer deposited onto a glass substrate. A 4 nm thick silver layer below the percolation threshold was located either between silicon and ITO or on top of the silicon film. First measurements with the silver island film at the silicon-ITO- interface show local variations of the change of the tunneling current on top of the silicon layer if the intensity of the light (820 nm wavelength) is varied. The contrast is influenced by the topography but not consistently, which is a hint to the influence of the hidden metal island film. Intensity-dependent U-I-characteristics were analyzed in order to deconvalve the serial tunneling and photo resistances of the sample.