Nanoscale Mass-Spectrometry Imaging of Grain Boundaries in Perovskite Semiconductors

Incorporation of alkali metals such as Cs+, Rb+, and K+ into hybrid organic-inorganic halide lead perovskites (HOIPs) generally improves the optoelectronic properties of HOIPs. However, it is still uncertain how alkali metals interact and distribute within the HOIPs. There is also a struggle in finding a technique for nanometer-scale structural and chemical characterization without laborious sample preparation or risking severe beam damage of the material during characterization. Here, we have investigated the nanometer-scale distribution of alkali pairs (K-Cs, Rb-Cs, and K-Rb) incorporated into a HOIP using helium-ion microscopy coupled with secondary-ion mass spectrometry (HIM-SIMS) that allows for nanometer-scale elemental and morphological imaging at an unprecedented spatial resolution. HIM-SIMS analysis reveals that Rb segregates at perovskite grain boundaries irrespective of whether it is paired with Cs or K.