Nano Crystals to Micro Crystals: Organolead Triiodide Perovskite Crystal Growth from Isopropanol Solution

Abstract

Perovskite-absorber solar cells have become a research area with high interest for their efficient energy conversion. A clue to the high performance of the material is the long diffusion length of charge carriers, which depend on crystallinity and morphology. However, still the main difficulty is to gain reproducible performance which address questions to the functions originating from the crystal chemistry in these materials. The first crystallographic information is commonly X-ray diffraction for organo-metal halide perovskites, but scattering is dominated by higher atomic elements, and is relatively insensitive to the organic component that controls the phase and crystal formation [1]. By combining different characterizations techniques as TEM, SEM, Raman, XRD and ED we study perovskite crystals formed from a mixture of both stoichiometric and non-stoichiometric II-propanol solution of methyl ammonium iodide and lead iodide. A comparison of different crystals with its electron and x-ray diffraction pattern gained knowledge in how the material is built up. It is seen how the atoms organize from small perovskite quantum dots to larger single crystals. The size and structure of the crystals can further be controlled by molar ratio, additives and temperature. Here we try to illuminate and explain the crystal structure birth and its organized growth of the perovskite grains. This is combined with optical characterization; UV/vis/NIR spectrophotometry and photoluminescence spectroscopy of the spin-coated solution on a substrate. The comparably environmental friendly II-propanol evaporates fast after spin-coating and large single crystal grains are formed. The combined results give new insight into the crystal chemistry of the perovskite solar cell material. Figure 1