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Aluminium-Doped Zinc Oxide Rear Reflectors for High-Efficiency Silicon Heterojunction Solar Cells
This contribution demonstrates an improved infrared response of the rear reflector of monofacial silicon heterojunction solar cells using aluminium-doped zinc oxide (AZO) in lieu of indium tin oxide (ITO) in the back electron-collecting shell. Along these lines, the carrier concentration and the thickness of the rear AZO layer are optimized in order to minimize the free-carrier and the plasmonic absorption losses without detrimentally affecting the selectivity and the electrical transport properties of the device. The respective reductions of free-carrier versus plasmonic absorption losses are thoroughly analyzed. Furthermore, the open-circuit voltage and series resistance of the solar cells are shown to not be impacted by the AZO thickness and the carrier concentration within the investigated ranges. As a result of these optimizations, a significant decrease in the parasitic absorption is obtained, leading to a champion device with a short-circuit current density of up to 40.81 mA/cm2 and an efficiency of 23.96%, featuring a standard screen-printed silver grid at the front with ca. 3.25% optical shadowing. In summary, AZO appears to be a promising indium-free alternative material to replace the back ITO commonly used in silicon heterojunction solar cells.

Authors: L.-L. Senaud,G. Christmann, A. Descoeudres, J. Geissbuhler, L. Barraud, N. Badel, C. Allebe, S. Nicolay, M. Despeisse, B. Paviet-Salomon, C. Ballif

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