Impedance spectroscopy study of tandem solar cells based on $c$-Si with a top layer perovskite nanocrystals CsPbBr$_3$ and CsPbI$_3$

The deposition of an additional layer of nanoparticles is a widely used method for improving optical and electrical characteristics of semiconductor solar cells (SCs). We present the results of studies of impedance spectroscopy (IS) in operating sandwich structures based on films of nanocrystals (NCs) of inorganic perovskites of lead halides CsPbI$_3$ and CsPbBr$_3$ deposited on the surface of a SCs based on crystalline silicon ($c$-Si). The IS results show that under identical conditions the Cole-Cole plots for both structures are in a good agreement with the equivalent circuit model and represents series resistance, recombination resistance and geometric capacitance, respectively, which arise due to charge accumulation, charge transfer resistance and/or additional interfacial electronic states. It was found that adding of the CsPbI$_3$ layer enhances the photo response under bias, but such a photo response leads to a decrease in conductivity. On the contrary, adding of the CsPbBr$_3$ layer blocks the photo response under bias but slightly improves the photo response for the zero bias. The obtained results provide the way to improve the performance of next generation of tandem c-Si SCs with perovskite NCs upper layers.