Solvothermal Modification of SnO₂ for Electron Transport Layers of Perovskite Solar Cells

SnO₂ has been widely used as an electron transport material in perovskite solar cells (PSCs), due to its high optical transmittance and high electron mobility. However, SnO₂ films prepared by using sol-gel method have poor crystallinity owing to the low preparation temperature. There are many defects in the films, which led to the recombination of the photoelectrons, thus reducing the photoelectric conversion efficiency (PCE). The SnO₂ electron transport layers (ETLs) were treated with deionized water, methanol, ethanol and isopropanol. The effects of solvothermal treatments on performance of SnO₂ ETLs and PSCs were studied. With XRD, SEM, contact angle, AFM, UV-Vis, J-V curves and IPCE, physical phase, morphology, roughness, optical performance and photoelectric performance of the samples were characterized. It is found that hydrothermal and solvothermal treatment can increase crystallinity of SnO₂ and visible transmittance of the films, thus enhancing the interfacial contact between ETLs and the perovskite layers. As a result, PCE of the PSCs were effectively improved. Photoelectric performance of the PSCs assembled with the hydrothermally treated SnO₂ was optimized, with the PCE of the cell to be 15.48%, which is 13.8% higher than the PCE (13.60%) of the untreated cell. In addition, the open-circuit voltage (V_oc) was 1.09 V, the short-circuit current density (J_sc) was 19.32 mA·cm⁻², and the fill factor (FF) was 73.18%.