Figure 1. Structure characterization and optical absorption spectrum.

(a) The microscopic image of the single crystal. The cross-hair indicates that the X-ray beam is located at the front face. Inset is the photograph of the single crystal. (b) X-ray diffraction pattern measured by two-dimensional area detector. The right and left frame are corresponding to 2θ centred at 30 and 60°, respectively. (c) Integration of the X-ray diffraction pattern. The diffraction intensity is integrated in the region of χ=90±5°, indicated by the black lines in panel b. χ is the angle between the plane determined by the incident and diffracted beams and the plane of the front face. (d) The absorption coefficient (red circles) of the CH₃NH₃PbBr₃ perovskite single crystal obtained from ellipsometry measurement. The black-line is the modelled absorption coefficient with excitonic (green-dash line) and continuum (blue-dash line) components.