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Properties of mixed phase silicon-oxide-based passivating contacts for silicon solar cells
We investigate the properties of an electron selective front contact based on a phosphorous doped mixed-phase SiOx/Si layer stack at device level. The addition of the SiOx phase to the Si layer targets reduced optical absorption, pursuing the goal of a broad-band transparent full-area passivating contact for front-side application. To demonstrate the validity of our approach we realised a planar hybrid solar cell with the mixed-phase SiOx/Sibased passivating contact on the front side and a hydrogenated amorphous (i/p) silicon heterojunction as rear hole-selective contact. With this structure, we obtained a V-oc of 691 mV, a Jsc of 33.9 mA/cm(2), a fill factor of 79.4% and an efficiency of 18.6% on a planar n-type FZ Si-wafer. Temperature-dependent IV-measurements at solar cell level were performed in order to understand the physical mechanisms behind charge carrier transport and surface passivation of the mixed-phase SiOx/Si layer stack. The results were compared to those of a standard silicon heterojunction (SHJ) cell on a similar planar substrate. The temperature dependence of the IV-curves in the range from-100 degrees C to and75 degrees C reveals that the hybrid cell is less temperature sensitive with respect to the SHJ cell. Furthermore, at low temperatures, the analysis reveals a reduction of the voc temperature coefficient of the hybrid cell, whereas for the SHJ cell a saturation occurs. This behaviour hints that the barrier imposed by the SiOx/Si-based contact is less pronounced than the barrier imposed by a standard SHJ contact.

Authors: I. Mack, J. Stuckelberger, P. Wyss, G. Nogay, Q. Jeangros, J. Horzel, et al.

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