Automated wideline nuclear quadrupole resonance of mixed-cation lead halide perovskites

Abstract. Nuclear quadrupole resonance (NQR) is a sister technique to NMR that is extremely sensitive to local crystal composition and structure. Unfortunately, in disordered materials this sensitivity also leads to very large linewidths, presenting a technical challenge and requiring a serious time investment to get a full spectrum. Here we describe our newly developed, automated NQR setup to acquire high-quality wideline spectra. Using this setup, we carried out ¹²⁷I NQR on three mixed cation lead halide perovskites (LHPs) of the form MA_xFA_1−xPbI₃ (MA = methylammonium, FA = formamidinium, x = 0.25,0.50,0.75) at various temperatures. We achieve a signal-to-noise of up to ~ 400 for lineshapes with a full-width-half-maximum of ~ 2.5 MHz acquired with a spectral width of 20 MHz in the course of two to three days. The spectra, which at least partially exhibit features encoding structural information, are interpreted using a statistical model. This model finds a degree of MA–MA, FA–FA clustering (0.2 ≤ S ≤ 0.35). This proof-of-principle for both the wideline NQR setup and the statistical model widens the applicability of an underutilised avenue of non-invasive structural research.