Probing Perovskite Inhomogeneity beyond the Surface: TOF-SIMS Analysis of Halide Perovskite Photovoltaic Devices.

Understanding the origins and evolution of inhomogeneity in halide perovskite solar cells appears to be a key to advancing the technology. Time-of-flight secondary-ion mass spectrometry (TOF-SIMS) is one of the few techniques that can obtain chemical information from all components of halide organic-inorganic perovskite photovoltaics in one-dimension (standard depth profiling), two-dimensions (high-resolution 100 nm imaging), as well as three-dimensions (tomography combining high-resolution imaging with depth profiling). TOF-SIMS has been used to analyze perovskite photovoltaics made by a variety of methods, and the breadth of insight that can be gained from this technique is illustrated here including: cation uniformity (depth and lateral), changes in chemistry upon alternate processing, changes in chemistry upon degradation (including at interfaces), and lateral distribution of passivating additives. Using TOF-SIMS on multiple perovskite compositions, we show that the information regarding halide perovskite formation as well as inhomogeneity critical to device performance can be extracted providing one of the best proxies for understanding compositional changes resulting from degradation. We also describe in detail the measurement artifacts and recommend the best practices that enable unique insight regarding halide perovskite solar cell materials and devices.