Indium‐Free Recombination Layer for Perovskite‐Based Multijunction‐Solar‐Cells‐ with Improved Performance Using Sputtered Zinc Tin Oxide

Monolithic two-terminal perovskite-based multijunction solar cells are considered as the next generation technology in the photovoltaic market, thanks to their high power conversion efficiency at potentially low production costs. In these structures, an interlayer is required for subcell interconnection. Commonly used recombination layers are based on scarce and expensive materials such as gold or indium. Developing alternative candidates without compromising device performance is therefore crucial for the future of such multijunction technologies. Herein, low-temperature sputtered zinc tin oxide (ZTO) is employed as an indium-free recombination layer between two perovskite subcells. ZTO is deposited using scalable in-line sputtering. Slight zinc doping of tin oxide is needed to enable the DC sputtering from a rotary target. Employing ZTO results in improved device performance compared to the reference devices with indium tin oxide recombination layer, deposited via a lab-type sputtering tool. Perovskite/perovskite/silicon triple-junction and all-perovskite tandem solar cells show increased open-circuit voltages by ≈60 and ≈30 mV, respectively. The work showcases that ZTO can be sputtered in a non-destructive and scalable manner in different perovskite-based multi-junction technologies.