Highly efficient monolithic perovskite/CIGSe tandem solar cells on rough bottom cell surfaces

We present a new strategy for highly efficient perovskite/CIGSe monolithic tandem solar cells, fabricated directly on top of a rough CIGSe surface. This was enabled by conformally depositing the metal oxide NiOx by atomic layer deposition, as confirmed by TEM/EDX measurements. The resulting limiting NiOx/perovskite interface was improved by spin-coating additional thin layer of p-type polymer PTAA, thus forming a NiOx/PTAA hole selective bilayer. The fabricated tandem device has a 21.6% power conversion efficiency on 0.778 cm2, stable over 10 minutes of maximum power point tracking. The device performance is further analyzed by absolute photoluminescence measurements from which a VOC contribution of each subcell to the tandem VOC can be estimated.