Solvent Effect on Morphological, Crystalline and Electronic Properties of Triple-Cation Lead-Tin Double-Halide Perovskite Thin Films and Their Air Stability

Abstract

Recently, triple cation Cs/MA/FA and mixed halide Br/I lead perovskites were found to improve the stability and efficiency of perovskite solar cells. However, the replacement of Pb with Sn has not been fully developed. In this work, we focused on the investigation of the solvent effect on morphological, crystalline and electronic properties of the perovskite thin films with the compositions of Csx(MA0.17FA0.83)1-xPb1-ySny(I0.83Br0.17)3, where x = 0.05, 0.1, and 0.2 and y = 0, 0.25, 0.50 0.75, and 1.0. By optimizing the mixed solvents in making perovskite precursor solutions, anti-solvent volumes in wash step and annealing temperature, as well as adding anti-oxidation agent, we were able to fabricate pinhole-free perovskite thin films with shiny, uniform dark- color. The surface morphology, crystal structure and optical band gap were investigated using scanning electron microscope (SEM), X-Ray diffraction (XRD), and UV-Vis absorption spectroscopy. The air stability of the perovskite thin films was also assessed by acquiring SEM images and XRD patterns after the films were stored in an ambient condition for 10 days. Phase segregation occurred as shown in XRD peak shifts and white rods around grain boundaries in SEM images, which contain high Sn, Br, and F elements.