Mrs. Sara Jäckle Photo: MPG/Björn Hoffmann
(August 17, 2015) An HZB team headed by Prof. Silke Christiansen has made a surprising discovery about hybrid organic/inorganic solar cells. Contrary to expectations, a diode composed of the conductive organic PEDOT:PSS and an n-type silicon absorber material behaves more like a pn junction between two semiconductors than like a metal-semiconductor contact (Schottky diode).
Their results have now been published in the Nature journal Scientific Reports (doi:10.1038/srep13008) and could point the way toward improvements in hybrid solar cells.
The system they investigated is based on conventional n-type silicon wafers coated with the highly conductive polymer mixture PEDOT:PSS and displays a power conversion efficiency of about 14 %. This combination of materials is currently extensively investigated by many teams in the research community.
“We systematically surveyed the characteristic curves, the dark current as well as the capacitance of such devices using silicon wafers with different doping concentrations” explains Sara Jäckle, lead author of the article and Ph.D. student in Prof. Silke Christiansen’s team (HZB Institute of Nano-architectures for Energy Conversion and research group leader at the Max Planck Institute for the Science of Light MPL in Erlangen). “We learned that the characteristic curves in the dark as well as the open-circuit voltage of the solar cells are dependent on the doping concentration of the silicon wafer. This behaviour and the order of magnitude of the measured values do not correspond at all to those of a typical Schottky junction.”