We will discuss new approaches to studying hybrid (organic-inorganic) multi-cation lead halide perovskites which hold promise for a new generation of easily processable solar cells. We show how multi-nuclear solid-state NMR allows us to obtain an atomic-level picture of microscopic phase composition. The use of low temperature (~100K) allow us to rapidly obtain13C CP spectra with unprecedented sensitivity to elucidate the atomic level nature of mixed guanidinium- formamidinium and methylammonium perovskite phases. We provide the first atomic-level proof of guanidinium incorporation into 3D perovskites. Similarly, we use two-dimensional 1H-1H spin diffusion measurements to directly evidence the formation of 3D perovskites in hybrids with lower dimensionality structures. We also use 133Cs, 87Rb and 39K solid-state MAS NMR at high magnetic fields (up to 21.1 T) to probe microscopic composition of Cs-, Rb- and K-doped double-, triple- and quadruple-cation lead halides in bulk and in thin films. Contrary to previous reports, we find no proof of Rb or K incorporation into the 3D perovskite lattice in these systems. Instead, a number of Rb- and K-rich phases are formed, leading to changes in the iodide-to-bromide ratio in the perovskite phase. This finding rationalizes the K- and Rb-induced changes in the band gap observed using optical spectroscopies. Further, we introduce a general and straightforward method for confirming the substitutional doping of perovskite phases with paramagnetic dopants, such as transition metals and lanthanides. Using 133Cs and 1H solid-state MAS NMR relaxation measurements we provide for the first time direct evidence that Mn2+and Eu2+are incorporated into CsPbX3 perovskite lattices. We also show that, contrary to current conviction, Co2+is not incorporated into the perovskite lattice of MAPbI3.

Solid-state NMR approaches to lead halide perovskites

2019 Spring National Meeting

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