Growth of hopper-shaped CsPbCl crystals and their exciton polariton emission.

CsPbCl is an attractive wide-bandgap perovskite semiconductor. Herein, we have grown hopper-shaped CsPbCl crystals in a solution droplet dripped on a heated substrate. During the growth, we have observed the impacts of the coffee ring effect and Marangoni flow, which may result in the hopper shape. Their photoluminescence spectra feature double peaks, which are located at 413.9 nm and 422.0 nm, respectively, and the latter increases faster in intensity than the former as the excitation power increases. We believe that the higher-energy peak originates from the excitonic emission and the lower-energy one is from the polaritons' emission, where the polaritons are generated in the exciton-exciton inelastic scattering process. Based on such an explanation, the exciton binding energy of CsPbCl is estimated to be 76.7 meV in our experiments, consistent with the previous reports.