Automated wide-line nuclear quadrupole resonance of mixed-cation lead-halide perovskites

Abstract

Nuclear quadrupole resonance (NQR), a technique related to nuclear magnetic resonance, 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 set-up to acquire high-quality wide-line spectra. Using this set-up, we carried out 127I NQR on three mixed-cation lead-halide perovskites (LHPs) of the form MAxFA1-xPbI3 (where MA denotes methylammonium; FA denotes formamidinium; and xCombining double low line 0.25, 0.50 and 0.75) at various temperatures. We achieve a signal-to-noise ratio of up to 1/4400 for lineshapes with a full width at half maximum of 1/42.5MHz acquired with a spectral width of 20 MHz in the course of 2-3 d. 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 and FA-FA clustering (0.2≤S≤0.35). This proof-of-principle for both the wide-line NQR set-up and the statistical model widens the applicability of an underutilised avenue of non-invasive structural research.