Ultrasonic‐Assisted Wet Chemistry Synthesis of Ultrafine SnO2 Nanoparticles for the Electron‐Transport Layer in Perovskite Solar Cells

Abstract SnO 2 was recently employed as an efficient electron‐transport layer (ETL) in perovskite solar cells (PSCs) and high power conversion efficiencies (PCEs) have been reported. However, it is still challenging to fabricate SnO 2 thin films through facile solution‐based synthesis at low temperature (<150 °C) to be compatible with the large scale module fabrication, especially for flexible devices. Here, we report a low temperature solution‐based method for preparation of SnO 2 nanoparticles. Ultrasonic‐assisted wet chemistry synthesis of ultrafine SnO 2 nanocrystals with particle size ranging from 2 to 5 nm was achieved by employing a SnCl 4 ⋅5 H 2 O solution in a mixed ethanol–water solution and with no annealing step. The crystallinity and microstructure of the SnO 2 nanoparticles were investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM), as well as selected area electron diffraction (SAED) analysis. The added water in ethanol and increased pH values were demonstrated as two key factors to successful fabrication of highly crystallized samples with high reproducability. An efficiency of 16.56 % was achieved for PSCs based on SnO 2 nanoparticles synthesized by ultrasonic‐assisted wet chemistry.