X‐Ray and Neutron Diffraction on Materials for Thin‐Film Solar Cells

Abstract

In order to understand natural and artificially produced materials, a detailed understanding of their crystal structures is required. This information is a basis for research in physics, chemistry, biology, and materials science. Among the various experimental methods, neutron and X-ray (photon) scattering have become key techniques of choice. Both techniques are complementary. In X-ray scattering, it is almost exclusively the electrons in atoms which contribute to the scattering, whereas neutrons interact with the atomic nuclei. This has an important consequence: the response of neutrons from light atoms (such as hydrogen or oxygen) is much higher than for X-rays, and neutrons easily distinguish atoms of comparable (or even equal) atomic number (see Figure 13.1). Due to the fact that neutrons interact with atoms via nuclear rather than electrical forces and nuclear forces are very short-range (of the order of a few fermis, i.e., 10 À15 m), the cross section for such an interaction is very small. The size of a scattering center (nucleus) is typically 10 5 times smaller than the distance between such centers. As a consequence, neutrons can travel large distances through most materials without being scattered or absorbed. Thus, neutrons penetrate matter much more deeply than X-rays.While neutron scattering provides insights into the crystal structure with high resolution, X-ray scattering has the advantage that (due to a larger scattering cross section) measurement durations are usually much shorter, compared with neutron scattering. Additionally, lab-scale X-ray sources are broadly available. Diffraction of X-Rays and Neutron by MatterMost of all inorganic, solid materials can be described as crystalline. When X-rays or neutrons interact with a crystalline substance, coherent elastic scattering may occur which is also termed diffraction.

Interface Engineering for Highly Efficient and Stable Perovskite Solar Cells

“…[ 46 ] X‐ray diffraction (XRD)‐based characterization techniques, including conventional laboratory‐based XRD and synchrotron‐based grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) (Figure 2c), are widely used to provide information on a material's crystallographic structure, phases, preferred crystal orientations, chemical composition, and other physical properties related to the crystallinity of the material. [ 47 ] Performing XRD experiments, such as GIWAXS, in a synchrotron facility can provide additional microstructural information, such as depth‐dependent and quantitative film texture information, and in situ experiments can allow for a real‐time assessment of the evolution of the microstructure during processing. [ 42,47 ] Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are real‐space imaging techniques that are commonly utilized to characterize thin‐film morphology, such as surface coverage, grain size, and surface roughness.…”

“…[ 47 ] Performing XRD experiments, such as GIWAXS, in a synchrotron facility can provide additional microstructural information, such as depth‐dependent and quantitative film texture information, and in situ experiments can allow for a real‐time assessment of the evolution of the microstructure during processing. [ 42,47 ] Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are real‐space imaging techniques that are commonly utilized to characterize thin‐film morphology, such as surface coverage, grain size, and surface roughness. [ 48 ] Additional microstructural information can also be obtained through SEM characterizations, such as phase separation and distribution by detecting characteristic X‐rays or backscattered electrons.…”

Cationic point defects in CuGaSe2 from a structural perspective

“…9 The resulting cation site occupation factors (SOF) were used to further apply the method of average neutron scattering length. 7,10,11 This method was previously adopted to identify the type and concentration of point defects in offstoichiometric CuInSe 2 . 7 The average neutron scattering lengths b exp 4b values (except for x ¼ 0.82) are found to be within the value for b Ga .…”