Hybrid perovskite solar cells fabricated from guanidine hydroiodide and tin iodide.

For the search of new metal-halide perovskite solar cell materials, tolerance factors are calculated from the ionic radius of each site and are often utilized as the critical factors to expect the materials forming perovskite structure. As one of such amine hydrohalides, guanidine hydroiodide (GI) is reported not to react with PbI2. However, in this paper, we report the product of GI and SnI2 reaction, its visible light absorption, X-ray diffraction, and its solar cell operation, in spite of the more disadvantageous tolerance factor of SnI2 than PbI2. We also report the thermal stability of GI, enabling precise control of vacuum deposition, and utilization of co-evaporant induced crystallization method during the vacuum evaporation of the SnI2 film, which resulted in enlarging the SnI2 crystals and improving the short circuit current density of the solar cell.