Stable Inverted Perovskite Solar Cells with Efficiency over 23.0% via Dual-Layer SnO₂ on Perovskite

Perovskite solar cells (PSCs) have shown great potential for reducing costs and improving power conversion efficiency (PCE). One effective method to achieve the latter is to use an all-inorganic charge transport layer (ICTL). However, traditional methods for crystallizing inorganic layers often result in the formation of a powder instead of a continuous film. To address this issue, we designed a dual-layer inorganic electron transport layer (IETL). This dual-layer structure consists of a layer of SnO₂ nanocrystals (SnO₂ NCs) deposited via a solution process and a dense SnO₂ layer deposited through atomic layer deposition (ALD SnO₂) to fill the cracks and gaps between the SnO₂ NCs. PSCs having these dual-layer SnO₂ ETLs achieved a high efficiency of 23.0%. This efficiency surpasses the recorded performance of ICTLs deposited on the perovskite. Furthermore, the PCE is comparable to that achieved with a C60 ETL. Moreover, the high-density structure of the ALD SnO₂ layer inhibits the vertical migration of ions, resulting in improved thermal stability. After continuous heating at 85 °C in 10% humidity for 1000 h, the PCE of the dual-layer SnO₂ structure decreased by 18%, whereas that of the C60/BCP structure decreased by 36%. The integration of dual-layer SnO₂ into PSCs represents a significant advancement in achieving high-performance, commercially viable inverted monolithic PSCs or tandem solar cells.