Toward the working mechanisms of tin oxide as buffer layer in perovskite/silicon tandem solar cells

Tin oxide (SnOX), a buffer layer commonly used to protect both the electron transport layer and the perovskite layer from sputtering-induced damage during the deposition of transparent conductive oxide in the top cell of perovskite-related tandem solar cells, is considered essential for achieving high efficiencies. Here, we systematically investigate the impact of SnOX on single-junction perovskite solar cells to understand the working mechanism of SnOX in the perovskite top cells. We discuss the correlation between the SnOX process and the photovoltaic parameters using steady-state photoluminescence, external quantum efficiency, space-charge-limited current measurements, and numerical simulations. We observe that the efficiency increased with thicker SnOX and the results suggest that thicker SnOX not only decreases the series resistance of perovskite solar cells but also has the potential to suppress nonradiative recombination. The improved buffer layer is finally used to produce a perovskite/silicon tandem solar cell with an efficiency of 32.84% (with a corresponding efficiency of 31.81% calculated using the short-circuit current density from the external quantum efficiency measurements).