SnO2/2D-Bi2O2Se new hybrid electron transporting layer for efficient and stable perovskite solar cells

Interfacial engineering has been proved to be an effective way to enhance the performance of perovskite solar cells (PSCs) by reducing interfacial charge recombination. In this work, two-dimensional (2D) Bi2O2Se nano-flakes with high charge mobility are synthesized by facile composited molten salt method, and used as electron transport layer (ETL) of PSCs for the first time. The PSCs based on single 2D Bi2O2Se nanoflakes ETL exhibit power conversion efficiency (PCE) of 9.12%, which is 110% higher than those without ETL (4.32%). To fill pinholes and defects on the surface of SnO2 thin film, we also use the 2D Bi2O2Se nanoflakes to modify the surface of SnO2 thin film, and fabricate SnO2/2D-Bi2O2Se new hybrid ETL to effectively reduce recombination at hetero-interface. Owing to the high charge mobility of 2D Bi2O2Se nanoflakes and cascade band alignment between perovskite active layer and tin dioxide, more efficient electron transport in PSCs is obtained than the single SnO2 ETL. Moreover, novel hybrid ETL provides a smoother and more hydrophobic surface for larger perovskite crystal formation. Compared with PSCs with single SnO2 ETL, the PCE of PSCs based on SnO2/2D Bi2O2Se hybrid ETL is improved to 19.06% from 16.29% with suppressed hysteresis. More interesting, the stability of PSCs with the new hybrid ETLs is also improved due to the improved crystallinity of perovskite active layer. This work shows the 2D Bi2O2Se material has potential for applications in PSCs.