Hybrid perovskites have generated a great deal of interest because of their potential in photovoltaic applications. However, the toxicity of lead means that there is interest in finding a nontoxic substitute. Bulk single crystals of both cubic CH3NH3 SnI3 and CH(NH2)2 SnI3 were obtained by using the top-seeded solution growth method under an ambient atmosphere. Structural refinement, band gap, thermal properties, and XPS measurements of CH3NH3 SnI3 and CH(NH2)2 SnI3 single crystals are also reported in detail. These results should pave the way for further applications of CH3NH3 SnI3 and CH(NH2)2 SnI3.

Hybrid perovskites have generated ag reat deal of interest because of their potential in photovoltaic applications. However,t he toxicity of lead means that there is interest in finding anontoxic substitute.Bulk single crystals of both cubic CH 3 NH 3 SnI 3 and CH(NH 2 ) 2 SnI 3 were obtained by using the top-seeded solution growth method under an ambient atmosphere.Structural refinement, band gap,thermal properties,and XPS measurements of CH 3 NH 3 SnI 3 and CH(NH 2 ) 2 SnI 3 single crystals are also reported in detail. These results should pave the wayf or further applications of CH 3 NH 3 SnI 3 and CH-(NH 2 ) 2 SnI 3 .Lead-containing organic-inorganic hybrid perovskite materials are of great interest for photovoltaic applications. [1] Increases in power conversion efficiencies (PCEs) from 3.8 % [2] to 20.1 % [3] have been reported over the past six years.S ince the toxicity of lead is of concern, an ontoxic substitute for perovskite materials is required. TheP bc ould be replaced with Sn or Ge,which are in the same group in the periodic table.H owever,t he stability of the 2 + oxidation state decreases on descending the group,s ot hese materials may not be stable. [4] Recent reports [4][5][6][7][8] on CH 3 NH 3 SnI 3 (MASnI 3 )a nd CH-(NH 2 ) 2 SnI 3 (FASnI 3 )m aterials mainly focus on hybrid tin halide perovskite polycrystalline and thin films.T othe best of our knowledge,t here are few previous reports on solar cells using Sn-based perovskite materials as the absorber layer, although PCEs from about 6% to 8.5 %h ave been reported by Kanatzidis, [5,6,15] Snaith, [4] and their respective co-workers. On the other hand, single crystals are important for studies of the basic properties of materials in the absence of grain boundary effects.T here have been many questions about the lower PCEs and stability of tin iodide perovskite materials. Most of the previous reports on the properties of MASnI 3 and FASnI 3 used single crystals that were synthesized and grown under inert (Ar or N 2 )a tmospheres, [7][8][9][10][11][12][13][14] There were no reports on the growth of bulk MASnI 3 and FASnI 3 single crystals under an ambient atmosphere,b ecause of the instability of these materials.W eh ave obtained both cubic MASnI 3 and FASnI 3 single crystals with dimensions of 20 mm 16mm10 mm and 8mm6mm5mm( Figure 1) under an ambient atmosphere by using the topseeded solution growth (TSSG) method. Detailed structural refinements and measurements of the band gap and thermal properties of MASnI 3 single crystals have also been carried out. Thebandgaps of MASnI 3 and FASnI 3 single crystals are approximately 1.15 eV and 1.4 eV,r espectively.T he crystals exhibit relatively good physical and chemical stability when exposed to inert atmospheres.T he thermal expansion coefficients a 11 of MASnI 3 and FASnI 3 along all the axial directions were calculated to be 3.423 10 À5 K À1 and 3.667 10 À5 K À1 ,r espectively.T hese properties of MASnI 3 and FASnI 3 single crystals pave the way for further applications in optoelectronics...