Chapter 24: Microscopic Electrical Characterization of Inorganic Semiconductor-Based Solar Cell Materials and Devices Using AFM-Based Techniques

Atomic force microscopy (AFM)-based microscopic electrical techniques provide new insights into the characterization of electronic devices, which is useful for understanding device physics and improving device performance. This chapter introduces the fundamentals of some major AFM-based electrical techniques, including scanning Kelvin probe force microscopy (SKPFM), scanning capacitance microscopy (SCM), and conductive AFM (C-AFM), and reviews some recent characterization studies on inorganic semiconductor solar cell materials and devices. A potential measurement on junctions of solar cells presents SKPFM as a powerful tool for two-dimensional junction location identification by direct electrical measurement. The potential measurement further reveals electrical field distributions under bias voltages that relate to the defects on the junctions. Grain boundaries (GBs) of polycrystalline thin-film materials are characterized by measuring carrier depletion or band bending using SCM and SKPFM, which provide the measurements of individual GBs and are thus able to correlate the GB electrical properties directly to the GB structure. Structural and electrical properties of a-Si:H and nc-Si:H thin films and devices are also characterized through a prototype structure of a-Si:H and nc-Si:H mixed phase. Localized electrical properties on the nc-Si: H phase, and phosphorus and boron doping effects on the film structure are reviewed.