Perovskite solar cells based on nanocrystalline SnO₂ material with extremely small particle sizes

In this work, we report the synthesis of SnO2 nanocrystalline material and its application in perovskite solar cells. The material has been characterised comprehensively by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area diffraction, and N2 adsorption analysis. The results have revealed that the average particle size of the SnO2 material was less than 3nm, resulting in a large specific surface area of 173.9m²g^-1. The investigation of the material in perovskite solar cells as electron-transport layer showed that pure SnO2 material did not favour the photovoltaic performance of the device. The best solar cell obtained with one layer of SnO2 film (22nm) showed an energy conversion efficiency of 2.19% under an illumination intensity of 100mWcm-2. Beyond this thickness, the performance of the solar cells decreased significantly with increasing thickness of the SnO2 film due to a dramatic decrease in the photocurrent density. Nevertheless, it has been found that SnO2 material containing a small amount of metal tin (1.3%) significantly improved the performance of the solar cell to 8.7%. The possible reason for this phenomenon has been discussed based on the consideration of the energy band alignment of materials in the perovskite solar cells.