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HL: Fachverband Halbleiterphysik
HL 71: Energy materials: Silicon-based photovoltaics
HL 71.4: Vortrag
Mittwoch, 2. April 2014, 15:45–16:00, POT 151
Subnanometer thin silicon oxide films for the application as passivating interlayer in silicon heterojunction solar cells — •Wenjia Lu, Caspar Leendertz, Heike Angermann, Lars Korte, and Bernd Rech — Helmholtz-Zentrum Berlin, Institute for Silicon Photovoltaics, Kekuléstr. 5, 12489 Berlin, Germany
Subnanometer thin silicon oxide (SiOx) has previously been applied as interlayer between crystalline silicon (c-Si) wafers and hydrogenated amorphous silicon ((p)a-Si:H). To optimize such thin SiOx passivation layers, oxidations on silicon wafers with different crystal orientations were performed by different oxidation methods. Native oxide and wet-chemical oxides of different thickness and after different chemical wafer pre-treatment processes are compared. The layer thickness (dox) was measured with spectral ellipsometry, while field-dependent photovoltage measurements and minority charge carrier lifetimes have been applied in order to assess the interface passivation quality and to determine the interface defect density (Dit) and charge (Qit). For the native oxides a correlation between the defect density and the charge indicates that the overall charge is dominated by electrons trapped in defects. This relationship cannot be found for the wet-chemical oxides which show superior passivation quality. The highest passivation quality is obtained for the (111) surfaces after NH4F pre-treatment for SiOx layers of only 0.5 nm thickness. With a low Dit, a negative Qit that supports emitter band bending and a low thickness, this wet-chemical oxide seems most suitable to be used as a buffer layer between the n-type c-Si absorber and the (p)a-Si:H emitter.