Synthesis and Characterization of Lead-Free (CH3)3SSnI3 1-D Perovskite
We report on the preparation, crystal structure and spectral properties of the trimethylsulfonium tin triiodide perovskite, (CH3)3SSnI3. The air-sensitive lead-free perovskite compound is prepared by reacting the (CH3)3SI and SnI2 solid precursors in evacuated silica tubes at 100°C. According to powder x-ray diffraction and Rietveld analysis, (CH3)3SSnI3 crystallizes at room temperature in hexagonal symmetry and forms a 1D network of face-sharing [SnI6] octahedra along the c axis. UV–Vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 2.85 eV accompanied by a weak luminescence signal. Multi-temperature Raman spectroscopy reveals a fully reversible structural phase transition just below 0°C related to the reduction of the unit cell symmetry. Comparison with the widely studied Cs-, CH3NH3- and (NH2)2CH-based 3D-perovskites that are commonly used in third generation solar cells confirms the higher stability of (CH3)3SSnI3. This is attributed to the beneficial role of the bulky trimethylsulfonium group in the ASnI3 structure.