Organolead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) have recently gained much attention due to their high conversion efficiency (~20%), optical properties, low cost, solution processability, and long electron-hole diffusion lengths. Organolead mixed-halide perovskites (CH3NH3PbX3-aX’a, X, X’ = I, Br, Cl) are also of interest due to their tunable band gap and enhanced moisture stability. When CH3NH3PI3-xBrx is synthesized directly from solution, significant deviation from linear behavior between the halide loading and both the lattice parameter and absorption edge results. This trend is not observed for the CH3NH3PbBr3-xClx system synthesized directly from solution. These results were investigated by x-ray diffraction (XRD), diffuse reflectance, and 207Pb solid-state nuclear magnetic resonance (ssNMR) spectroscopy. 207Pb ssNMR detected the presence of additional phases in the as-prepared samples synthesized from solution. In order to observe what happens to these additional phases when the temperature is increased, these samples were subjected to annealing at different temperatures and the results were compared to samples prepared by physically mixing solids of the single-halide perovskites followed by annealing under the same conditions. The effects of annealing were studied by XRD, diffuse reflectance, 207Pb ssNMR, simultaneous thermogravimetric analysis and differential thermal analysis (STD), and scanning electron microscopy (SEM). All results were then rationalized based on the reactivity of the precursor solutions and the ease of forming a solid solution.

Perovskite mysteries revealed: Amorphous and dopant phases studied by annealing, 207Pb ssNMR, and XRD

251st National Meeting (2016)

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