Dynamic Nuclear Polarization of Inorganic Halide Perovskites

The intrinsic low sensitivity of nuclear magnetic resonance(NMR)experiments limits their utility for structure determination of materials.Dynamic nuclear polarization (DNP) under magic angle spinning (MAS)has shown tremendous potential to overcome this key limitation, enablingthe acquisition of highly selective and sensitive NMR spectra. However,so far, DNP methods have not been explored in the context of inorganiclead halide perovskites, which are a leading class of semiconductormaterials for optoelectronic applications. In this work, we studycesium lead chloride and quantitatively compare DNP methods basedon impregnation with a solution of organic biradicals with dopingof high-spin metal ions (Mn2+) into the perovskite structure.We find that metal-ion DNP provides the highest bulk sensitivity inthis case, while highly surface-selective NMR spectra can be acquiredusing impregnation DNP. The performance of both methods is explainedin terms of the relaxation times, particle size, dopant concentration,and surface wettability. We envisage the future use of DNP NMR approachesin establishing structure-activity relationships in inorganicperovskites, especially for mass-limited samples such as thin films.