Shaping the Band Structure of n-type Cs2SnI6Thin Films Using Electron Spectroscopy

Vacancy ordered double perovskites with better stability and eco-friendly composition are emerged as a new candidate for solar cells in the recent years. Cs
2
SnI
6
is one of the attracting materials in this group having a bandgap of ~ 1.48 eV. In the present work, thin films of Cs
2
SnI
6
are prepared using co-evaporation method in vacuum conditions followed by thermal treatment under iodine atmosphere. Cubic double perovskite structured n-type Cs
2
SnI
6
having a grain size of 0.4 µm is obtained through this process. Polygon shaped surface morphology is observed in the films. The electronic band structure of the material is determined using a combination of different electron spectroscopic techniques, viz reflected electron energy loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The bandgap of Cs
2
SnI
6
thin film is calculated by extrapolating the onset of the loss peak in REELS spectrum, which give a value of 1.5 eV. The work function and valence band maximum are estimated to be 4.9 and 6.31 eV respectively from UPS. The core elements and their oxidation states are identified using XPS which confirms the purity of Cs
2
SnI
6
phase. In addition, the valence band spectra are obtained using X-ray photoelectron spectroscopy. Two regions above the Fermi levels are identified in the valence band spectra, first one being comprised of the I p and Sn d states, the contribution from Sn d state being dominant. The secondt band have contribution from all Cs, Sn, I elements and results from the mixing of d, s, and s/p/d states respectively.