2, Hunan University, Changsha, Hunan, China
3, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Organic lead halide perovskites have shown immense potential in high-performance optoelectronic devices. However, significant challenges remain for real-world applications. A fundamental understanding of how the organic cations within inorganic framework affect the structural phase transitions, and optoelectronic properties of the organic-inorganic hybrid perovskite (OIHP) materials is desirable to design new materials and improve device performance. We have used the TOPAZ instrument at the ORNL Spallation Neutron Source to probe the role of hydrogen bonding in structural phase transition of OIHPs by collecting the 3D volume of diffraction pattern from the sample in neutron event mode. In this presentation, I will show our most recent result from real-time in situ variable temperature study that established the path of the organic cation induced anomalous optoelectronic phenomenon  in MAPbX3, where MA is methylammonium, an organic cation that forms a network of hydrogen bonds with the halides X (Br-, l-) in the solid states [1-2]. Data from real-time single-crystal neutron diffraction following the initiation of orthorhombic-tetragonal phase transition provided details the change of hydrogen bonding pattern between the organic donor and the inorganic accepter, which not only induces the structural transition that results in anomalous red-shift of PL peak position as temperature increases, but also causes the decrease in dielectric screening, leading to the reduction of non-radiative recombination for stronger PL intensity .
 Yang, B.; Ming, W.; Du, M. H.; Keum, J. K.; Puretzky, A. A.; Rouleau, C. M.; Huang, J.; Geohegan, D. B.; Wang, X. P.; Xiao, K. Manuscript submitted for publication.
 Ren, Y.; Oswald, I. W. H.; Wang, X.; McCandless, G. T.; Chan, J. Y. Crystal Growth & Design 2016, 16 (5), 2945-2951.