Scientists make solar cell losses visible

A team of scientists from the Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) and the University of Utah, USA, have experimentally demonstrated the way in which solar cells combined with selective contacts made of amorphous silicon (a-Si:H) generate loss currents at the nanometer scale. Using a scanning microscope, they scanned the solar cell surfaces in ultra-high vacuum, and demonstrated »tiny, nanometer-sized channels for the detrimental dark currents that are due to disorder in the a-Si:H layer.« Klaus Lips at HZB, working with a team led by Christoph Boehme at the University of Utah, was able to elucidate the processes at the interface on a nanometer scale for the first time using solar cells fabricated at PVcomB.
The physicists scanned the current flow through the selective a-Si:H contact and observed how »dark current channels with diameters of a few nanometers formed with increasing voltage leaky spots,« which reduce efficiency, according to HZB.
»The current channels are the fingerprint of local defects in the amorphous silicon, which the dark current uses as a sort of digging aid to dig its way through the amorphous contact layer,« explains Lips: »This is the first time that such conditions and processes have been made visible in a real working solar cell of the highest quality.« The results expanded »the understanding of how the efficiency of silicon solar cells can be improved in an even more targeted manner,« says Bernd Stannowski, who is responsible for the development of industrial silicon heterojunction solar cells at HZB.
© PHOTON

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