Neutron and X-Ray Scattering Studies of Metal Halide Perovskites

Metal halide perovskites (MHPs) are promising materials for photovoltaic and light-emitting devices. Studies on both powder and single-crystal forms of MHPs, under various conditions such as temperature and doping, reveal their dynamic nature and implications for device efficiency. Among MHPs, two-dimensional hybrid organic-inorganic perovskites (HOIPs) offer enhanced stability compared to three-dimensional counterparts. Using time-of-flight neutron spectroscopy, we identified distinct vibrational and rotational dynamics in two different 2D HOIPs. Our comparative analysis shows that organic molecule rotations suppress photoluminescence quantum yield (PLQY), while vibrations have a lesser impact. This suggests that rotational motions may reduce exciton binding energy, leading to higher non-radiative recombination rates.

Doping also plays a significant role in the light-emitting efficiency of MHPs, which is crucial for applications like radiation detection in scintillators. Using small-angle neutron scattering on quantum dot (QD)-loaded fully inorganic MHPs, we quantified QD distribution within the perovskite matrix and linked it to luminescence sensitivity. The structural dynamics of MHPs, particularly with temperature variations, can induce local disorder. This was explored through X-ray diffuse scattering and inelastic neutron scattering on single crystals of a 3D HOIP. We observed overdamped transverse acoustic phonons during the orthorhombic-to-cubic phase transition, which may lead to halide ion diffusion, increased phonon scattering, and reduced charge carrier stability. Together, these studies enhance our understanding of MHPs and provide insights to support the development of more efficient materials for light-emitting and photovoltaic applications.