Mechanically Robust and yet Electrically Conductive C60-SnO₂Electron Transporting Bilayer in Stable Perovskite Solar Cells

Inverted-type perovskite solar cells (i-PSCs) have demonstrated superior power conversion efficiencies (PCEs). The bilayer of C60-SnO₂as an electron transport layer (ETL) is often used in i-PSCs. It is known, however, that the interface is quite fragile mechanically under thermal cycling. For long-term stability, the interface between the bilayer should be refined. Herein, we propose a surface treatment method on C60 to enhance the mechanical robustness between the ETL bilayer and promote efficient electron transport. The deposition of SnO₂by atomic layer deposition on ozone-treated C60 surfaces led to a reduced incubation time, as evidenced by an increase in growth per cycle (GPC) with proper ohmic contact and effective charge extraction. The treatment with O₃also significantly enhanced the interface adhesion between C60 and SnO₂, which was confirmed through mechanical delamination tests and further analyzed via X-ray photoelectron spectroscopy (XPS). Consequently, the PCE of i-PSCs was 21.5% for untreated samples and 21.9% for those with the O₃treatment. The i-PSCs retained 91.9% of their initial performance under 1 sun illumination maximum power point operation for 2000 h in ambient condition. This work highlights the effectiveness of surface modification at the C60-SnO₂interfaces as ETLs in i-PSCs, leading to enhanced efficiency and stability.