Controlled synthesis of lead-free perovskite Cs2SnI6 as hole transport layer in dye sensitized solar cells

Abstract

Hybrid organic-inorganic perovskite material is undergoing rapid expansion over the past few years due to their application in solar cells. In particular, tin (Sn)-based perovskite has been considered to replace lead (Pb)-based perovskite because of toxic issues and it can cause adverse environmental impact. Cesium tin halide based perovskite (Cs2SnI6) material appears promising for large scale module fabrication and also oxygen and moisture stable because of high oxidation state of tin. In this study, we successfully synthesized Cs2SnI6 perovskite by mixing process of cesium carbonate (Cs2CO3) in hydriodic acid (HI) solvent and stannic iodide (SnI4) in ethanol solvent to form precipitate and all the processes was done in air and room temperature. Cubic crystal structure of perovskite was confirmed by X-ray Diffraction (XRD) measurement in comparison to the crystal structure of Pb-based perovskite. Scanning Electron Microscope (SEM) revealed morphology of Cs2SnI6 with the size of 0.4–5 mm. We controlled the solutions of Cs2SnI6 by mixing two kinds of solvent (gamma-butyrolactone and acetonitrile) with different volume ratio and the Cs2SnI6 thin films were confirmed by used of UV-vis spectrometer. The absorbance spectra give a characteristic two humps feature due to the specific band structure of Cs2SnI6 and it indicates the direct band gap about 2.8 eV.