| Autor: |
Koegel AA; Colorado State University, Department of Chemistry, Fort Collins, Colorado 80523-1872, United States., Mozur EM; Colorado State University, Department of Chemistry, Fort Collins, Colorado 80523-1872, United States., Oswald IWH; Colorado State University, Department of Chemistry, Fort Collins, Colorado 80523-1872, United States., Jalarvo NH; Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States., Prisk TR; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States., Tyagi M; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.; Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States., Neilson JR; Colorado State University, Department of Chemistry, Fort Collins, Colorado 80523-1872, United States. |
| Abstrakt: |
The emission of white light from a single material is atypical and is of interest for solid-state lighting applications. Broadband light emission has been observed in some layered perovskite derivatives, A 2 PbBr 4 ( A = R -NH 3 + ), and correlates with static structural distortions corresponding to out-of-plane tilting of the lead bromide octahedra. While materials with different organic cations can yield distinct out-of-plane tilts, the underlying origin of the octahedral tilting remains poorly understood. Using high energy resolution (e.g., quasi-elastic) neutron scattering, this contribution details the rotational dynamics of the organic cations in A 2 PbBr 4 materials where A = n -butylammonium ( n BA), 1,8-diaminooctammonium (ODA), and 4-aminobutyric acid (GABA). The organic cation dynamics differentiate ( n BA) 2 PbBr 4 from (ODA)PbBr 4 or (GABA) 2 PbBr 4 in that the larger spatial extent of dynamics of n BA yields a larger effective cation radius. The larger effective volume of the n BA cation in ( n BA) 2 PbBr 4 yields a closer to ideal A -site geometry, preventing the out-of-plane tilt and broadband luminescence. In all three compounds, we observe hydrogen dynamics attributed to rotation of the ammonium headgroup and at a time scale faster than the white light photoluminescence studied by time-correlated single photon counting spectroscopy. This supports a previous assignment of the broadband emission as resulting from a single ensemble, such that the emissive excited state experiences many local structures faster than the emissive decay. The findings presented here highlight the role of the organic cation and its dynamics in hybrid organic-inorganic perovskites and white light emission. |
