"Three Dimensional Nanoscale Properties of Photovoltaic and Electrically Functional Materials"
Nano- and meso- scale materials properties are crucial to the macroscopic performance of a wide range of photovoltaic and electrically functional devices. Investigations with Atomic Force Microscopy of photoconductors, piezoelectrics, and dielectrics have proven important for elucidating the local influence of grain boundaries, orientation, strain, and other microstructural defects or heterogeneities. This is especially relevant for practical devices due to their sensitivity to 3-D structuring, sub-surface effects, or thickness dependencies—all of which are affected by microstructure, concentration, field gradients, etc. Accordingly, we have lately leveraged serial sectioning to achieve Tomographic AFM for volumetric materials property mapping. Voxels are finer than 10 nm3, and capable of distinguishing superlattice layers as fine as 16 unit cells. With polycrystalline photovoltaics such CdTe or MAPbI3, T-AFM literally uncovers new pathways to improve carrier separation via inter- and intra- granular defects (Luria, Nature Energy, 2017; Song, Nature Communications, 2020). For BiFeO3, Tomographic AFM confirms Kay-Dunn thickness scaling for ferroelectricity (Steffes, PNAS, 2018), and even co-located domain and current maps which together reveal sub-surface topological defects. Direct effects of lateral strain are resolved for nanostructured composites (Song, Advanced Functional Materials, 2021). Analyses of boundary curvature (ErMnO3, Advanced Materials, 2022) and ultrathin films (Bi5FeTi3O15, Nature Materials, 2023), as well as ultra-resolution surface lithography, will also be discussed. Such volumetric insight and control are increasingly important for engineering optimal performance and reliability of real-world, 3-dimensional, materials devices.
