X-ray diffraction is a powerful method of characterizing crystalline materials in a non-destructive manner. It is often used to identify and quantify crystalline phases by illuminating samples with a beam of X-rays and analyzing the distinctive diffraction patterns emitted from specific, irradiated crystal phases. In this article, we will look at how X-ray diffraction can be used to assess photovoltaic materials intended for use in solar cells.
The Basics of X-Ray Diffraction
X-ray diffraction is able to detect all elements, having detection limits of ~1% and a depth resolution falling between ~20 Angstroms to ~30 microns – subject to material properties as well as incidence angles of X-rays. Whether organic, biological, inorganic, microscopic or macroscopic, all crystalline materials possess distinct physical properties which are dependent on their atomic structures. As such, the determination of structure is critical in many disciplines.
X-ray diffraction patterns show the distinct composition of periodic atomic arrangements in a given material. To identify large, varying ranges of crystalline samples, a search of a standard database for X-ray powder diffraction patterns results in quick phase identification for a large amount of crystalline samples.
Here is a brief overview of the benefits of X-ray diffraction when it comes to identifying unknown minerals:
- X-ray diffraction offers extremely rapid results for crystallography, especially when combined with modern computational capabilities;
- It is a powerful tool in that X-ray crystallography can be deployed for an extremely broad scope of materials and disciplines with ease;
- X-ray diffraction offers high precision of results, enabling researchers to locate the positions of atoms within a crystal with insights into their chemical status and the extent of disorder;
- From an operational perspective, X-ray diffraction is desirable as it does not require a large amount of sample preparation and x-ray diffraction units are easily accessible.
X-Ray Diffraction Applications
X-ray diffraction has a number of uses with the most notable being for the identification of unidentified crystalline materials (such as inorganic compounds and minerals). This is beneficial in geology for the classification of rock formation and the compounds that make up rock.
X-ray diffraction also finds use in medical science, helping scientists to develop new pharmaceuticals and in understanding energy storage materials. It is also used for characterizing thin films, quantifying lattice mismatch across film and substrate in addition to inferring stress and strain.
But one of the most important commercial applications of X-ray diffraction is in the quality control of photovoltaics for solar applications.
X-Ray Diffraction Use in Solar Cells
One of the most widely used materials for thin-film solar cells, as well as cadmium telluride and amorphous silicon, is copper indium gallium selenide (CIGS). Solar cells made from these materials are more cost effective when compared with crystalline silicon as the amount of material required for manufacturing the solar cells is low.
Solar cells have lower cell efficiencies despite this as they exhibit less mature upscaling in comparison to crystalline silicon-based solar cells. CIGS materials are still studied to improve their properties, done through the use of chemical substitution and the design of interfaces of the solar cell layers. The structural and chemical composition of a product must be controlled to ensure the optimum quality performance as well as the thickness of the layers.
The most effective, convenient and simple solution for quality assurance and quality control processes in addition to sophisticated analyses can take place via X-ray diffraction working together with energy dispersive x-ray fluorescence spectroscopy.
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