HClO4-assisted fabrication of SnO2/C60 bilayer electron-transport materials for all air-processed efficient and stable inverted planar perovskite solar cells

In inverted planar perovskite solar cells (PSCs), fullerene (C-60) and its derivatives are widely utilized as electrontransport layer (ETL) materials, however, possess some drawbacks such as low electron mobility, interfacial degradation, and relatively inferior stability. In this work, we develop a facile thermal annealing-free hydrothermal route to synthesize high-crystalline SnO2 nanocrystals through controlling the crystallization process with HClO4. An interlayer of SnO2 nanocrystals is inserted between C-60 ETL and Ag electrode. The SnO2 interlayer can not only serve as an ETL to help improve electron extraction and transport but also act as a passivation/barrier layer to prevent oxygen and moisture ingress and ion migration. Based on the p-i-n structure of fluorine-doped tin oxide (FTO)/NiOx/MAPbI(3)/C-60/SnO2/Ag, the power conversion efficiency (PCE) of the champion device is up to 16.36% with almost negligible hysteresis. The unencapsulated inverted PSCs retain more than 80% of its initial PCE value after storage in atmosphere for 90 days (>2100 h), and degrade only about 20% its initial efficiency after 41 h under heating at 85 degrees C. More important, all the preparation processes are performed under ambient conditions. Our work provides a viable strategy for assembling highly efficient and stable inverted PSCs in the air.