An optimized synthetic procedure for preparing photostable nanocrystalline methylammonium lead halide materials is reported. The procedure was developed by adjusting the lead halide to methylammonium/octylammonium halide precursor ratio. At a high precursor ratio (1:3), a blue-shifted photoinduced luminescence peak is measured at 642 nm for CH3NH3PbI3 with 0.01 to 12 mJ pulsed-laser irradiation. The appearance of this peak is reversible over 300 min upon blocking the irradiation. In order to determine if the peak is the result of a phase change, in situ x-ray diffraction measurements were performed. No phase change was measured with an irradiance that causes the appearance of the photoinduced luminescence peak. Luminescence microscpectroscopy measurements showed that the use of a lower precursor ratio (1:1.5) produces CH3NH3PbI3 and CH3NH3PbBr3 perovskites that are stable over 4 min of illumination. Given the lack of a measured phase change, and the dependence on the precursor ratio, the photoinduced luminesce peak may derive from surface trap states. The enhanced photostability of the resulting perovskite nanocrystals produced with the optimized synthetic procedure supports their use in stable optoelectronic devices.
Available at: http://works.bepress.com/emily-smith/57/