Sputtered rear electrode with broadband transparency for perovskite solar cells

Due to their high efficiencies combined with simple and cost-effective device fabrication, perovskite solar cells are promising candidates as top cells in tandem devices. For this application, the perovskite solar cell must be highly transparent at near-infrared wavelengths such that sufficient light is transmitted to the narrow-bandgap bottom cell. We demonstrate perovskite solar cells featuring a sputtered amorphous indium zinc oxide (IZO) layer as broadband transparent rear electrode. This electrode absorbs less than 3% in the 400-1200 nm wavelength range, while having a sheet resistance of 35Ω/sq. We show over 9% efficient semitransparent perovskite solar cells with IZO sputtered directly on the sensitive organic charge transport layer. The efficiency can be raised up to 10.3% by inserting a thin molybdenum oxide buffer layer, mitigating sputter damage to the underlying organic layer. These cells show more than 60% average transmittance in the 800-1200 nm wavelength range, which makes them suitable top-cell candidates for tandem devices. Finally, we discuss the performance potential of this highly transparent rear electrode for four-terminal tandem devices.