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 vs. 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.