Inert Interlayer Secures Flexible Monolithic Perovskite/CIGS Tandem Solar Cells with Efficiency Beyond 21%

Since mature CIGS products inherently bear an aluminum-doped ZnO (AZO) transparent conductive layer, whether it is necessary to deposit another transparent conductive thin layer using other materials such as indium tin oxide (ITO), indium zinc oxide (IZO) still remains a basic open question. Here we demonstrate that deposition of an inert interlayer preceding fabrication of the perovskite top cell is essentially warranted because the AZO layer is shown to be destructive toward the perovskite thin films. Flexible monolithic perovskite/CIGS tandem photovoltaics with an IZO interlayer achieved a high-performing efficiency of 21.24% with substantially improved stability at elevated temperatures. The unencapsulated target tandem solar cell retained 80% of its initial efficiency after 120 min of continuous maximum power (MPP) point operation at ∼90 °C in ambient air, while the control tandem device without the IZO interlayer failed after ∼25 min of operation under the same conditions.