Properties of cesium tin iodide (Cs-Sn-I) systems after annealing under different atmospheres

The influence of the annealing conditions on Cs-Sn-I systems was investigated. Cs-Sn-I powders were prepared by crystallization process from aqueous solutions. The X-ray diffractogramms (XRD) revealed the growth of yellow orthorhombic CsSnI3 phase (Y-CsSnI3, space group Pnma) with stab-like crystallites (50200 mu m length, 3050 mu m thickness). The annealing at T = 180 degrees C (t = 8 h) under flowing nitrogen lead to the formation of black gamma-CsSnI3 phase (B-phase) with orthorhombic structure (space group Pnma) and stab-like crystallites (70100 mu m length, 510 mu m thickness). SnI2 and CsI as secondary phases have been detected after annealing at T = 550 degrees C for t = 1 h in nitrogen. The annealing in air at T = 150 degrees C (t = 8 h) gave rise to the cubic Cs2SnI6 phase (space group Fm3m) with homogeneous platelet-like crystallites (35 mu m length, 12 mu m width). XPS spectra of the CsSnI3 phase indicated an oxidation state of 2+, +1 and 1- for Sn-, Cs-ions and iodine anions respectively whereas the formation of Sn(II)-O, Sn(IV)-O and Cs-O binds has been observed after annealing in air. Optical absorption measurements indicated a direct band behavior of the black (1.21 eV) and Cs2SnI6-phases (1.22 eV). The photoluminescence (PL) emission spectra of the B-gamma-CsSnI3 phase showed PL peaks at 1057 nm, 845 nm (at T = 180 degrees C for t = 8 h) and at 1070 nm, 851 nm (at T = 550 degrees C for t = 1 h) respectively and a weak PL-emission at 1054 nm in the Cs2SnI6 phase. Layers of B-gamma-CsSnI3 phase with semiconducting behavior have been prepared by spin-coating under Ar-atmosphere. (C) 2017 Elsevier B.V. All rights reserved.