Growth of mixed-halide perovskite single crystals
Abstract
In this paper, systematic halogen doping of CH3NH3PbI3−xBrx and CH3NH3PbBr3−yCly 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 CH3NH3PbI3−xBrx and CH3NH3PbBr3−yCly crystals change linearly with the x(y) values. For the CH3NH3PbI3−xBrx 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 CH3NH3PbI3−xBrx and CH3NH3PbBr3−yCly 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 CH3NH3PbI3−xBrx (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 CH3NH3PbI3−xBrx and CH3NH3PbBr3−yCly crystals decreases with increasing x(y) values. Research on CH3NH3PbI3−xBrx and CH3NH3PbBr3−yCly single crystals would be helpful to reveal the inherent properties of perovskite materials.