Highly crystalline Zn₂SnO₄ nanoparticles as efficient electron-transporting layers toward stable inverted and flexible conventional perovskite solar cells

In this work, we have successfully utilized a facile hydrothermal method to prepare crystalline Zn₂SnO₄ nanoparticles (ZSO NPs) and applied them as an efficient electron-transporting layer (ETL) via a simple room-temperature solution process for perovskite solar cells (PVSCs). The superior semiconducting properties of this ZSO-based ETL enable an efficient (PCE: 17.7%) inverted p-i-n PVSC to be fabricated with respectable ambient stability. It can retain over 90% of its original PCE after being stored under ambient conditions for 14 days under 30 ± 5% relative humidity. Moreover, it also facilitates the fabrication of efficient conventional n-i-p PVSCs with a PCE of ∼14.5% and ∼11.4% achieved on a glass/ITO rigid substrate and PEG/ITO flexible substrate, respectively.