Growth of mixed-halide perovskite single crystals

Abstract

In this paper, systematic halogen doping of CH₃NH₃PbI_3−xBr_x and CH₃NH₃PbBr_3−yCl_y bulk single crystals that were grown in mixed organic solvents via the ITC (inverse temperature crystallization) method was performed. X-ray diffraction measurement results show that the lattice constants of CH₃NH₃PbI_3−xBr_x and CH₃NH₃PbBr_3−yCl_y crystals change linearly with the x(y) values. For the CH₃NH₃PbI_3−xBr_x crystals, cubic to tetragonal phase transformation was observed where the iodine content reaches a certain level. The comparison of UV-vis-NIR absorption and PL spectra of CH₃NH₃PbI_3−xBr_x and CH₃NH₃PbBr_3−yCl_y crystals shows that their absorption coefficients are contributed by direct and indirect bandgap transitions. Three kinds of mechanisms were involved in their radiative recombination, including direct emission, indirect emission and direct–indirect coexisting emission. The CH₃NH₃PbI_3−xBr_x (x = 1.64, 2.39, 2.81, 2.9) crystals were considered to be indirect band gap materials, since their band edges can be divided into two regions by a turning point. TG analysis shows that the beginning decomposition temperature of CH₃NH₃PbI_3−xBr_x and CH₃NH₃PbBr_3−yCl_y crystals decreases with increasing x(y) values. Research on CH₃NH₃PbI_3−xBr_x and CH₃NH₃PbBr_3−yCl_y single crystals would be helpful to reveal the inherent properties of perovskite materials.