Spray-assisted deposition of a SnO₂ electron transport bilayer for efficient inkjet-printed perovskite solar cells

Developing an efficient electron transport layer (ETL) through structural modification is essential to produce high-performance perovskite solar cell (PSC) devices. Specifically, the ETL should exhibit low defects, high optical transparency, and charge selectivity for ideal electron transport. Herein, we demonstrate (i) the low-temperature fabrication of tin oxide (SnO₂) ETLs with a bilayer structure, and (ii) inkjet-printing of triple-cation perovskite films. Through the combined use of spin-coating and spray deposition, the optimized SnO₂-bilayer ETL shows a nano-granule-textured surface, noticeably fewer defects, and a cascade conduction band position with the inkjet-printed perovskite film. The champion PSC device, based on the SnO₂-bilayer ETL and inkjet-printed perovskite film, recorded an outstanding power conversion efficiency (PCE) of ∼16.9%, which is significantly higher than the device based on the conventional SnO₂ ETL (PCE ∼14.8%). The improved photovoltaic performance of the SnO₂-bilayer-based device arises mainly from more efficient charge transport and suppressed recombination at the ETL/perovskite interface. The SnO₂-bilayer ETL and inkjet-printed perovskite films demonstrated herein can be potentially used for large-scale manufacturing of photovoltaic modules.