Progress in the Applications of Photovoltaic Functional Crystals and Ceramics

1. Introduction

With the progression of mankind and the development of technology, great strides have been made regarding the application of inorganic crystalline materials in a number of fields such as high-energy and nuclear physics, environmental and safety inspection, the optoelectronics and communication fields, energy, and aerospace engineering, particularly the industrialization of photovoltaic and detector materials, which has brought mankind’s knowledge of natural disciplines to an all-time high. This has further promoted interdisciplinary collaboration between the fields of optoelectronic functional devices, biomedical engineering, and materials science, and has prompted scholars to accelerate the in-depth study of the original mechanisms of the physical responses of these materials in these fields and the commercialization of such functional devices.

This Editorial refers to the Special Issue “Inorganic Crystalline Materials”. This Special Issue aims to highlight new opportunities and challenges for advancing the development of the Inorganic Crystalline Materials, focusing on crystal or film growth, characterization, structure refinement, modeling, device fabrication and measurements, and system testing, as well as corresponding research which is fundamental to the field.

After repeated correspondence between the reviewers and authors to ensure the reference value of the papers, a total of 10 articles were finally accepted. This provides a platform for academic exchange and keeps us abreast of the research results of our peers.

2. An Overview of the Published Articles

As we all know, medical imaging detection technology has developed rapidly in recent years. A number of detectors, including cardiac-specific SPECT systems, bone densitometers, CT imaging, and soft-tissue imaging techniques, etc., have been developed for the detection of Cadmium Zinc Telluride (CZT), all of which have increased the efficiency of detecting this compound exponentially, with improved system sensitivity and image quality, and have greatly improved the accuracy of diagnosis. Bin Yu et al. [1] investigated the growth characteristics of CZT thin films on different substrates using the near-space sublimation method. They found that films grown on a (111)-oriented CZT wafer show good reactions to nuclear radiation signals and can more effectively detect radiation from weak radiation sources compared to films grown on non-oriented CZT wafers and FTO substrates. This result suggests that substrate selection plays a crucial role in the development of thin-film devices in terms of film quality and even device performance. Mercury iodide crystals, a crystal material used for medical imaging, also have a long history in crystals research. Compared with CZT, mercury iodide crystals have advantages in terms of energy resolution, particularly for applications in mammography and digital X-ray imaging. This is likely the main reason why researchers have been focusing on mercury iodide crystals. Gang Xu et al. [2] reported the preparation of large-area mercury iodide thin-film imaging detectors and discussed the relationship between the deposition temperature and the quality of the film, creating a positive reference for further optimizing this process to obtain large-area thin-film devices for medical imaging and for the commercial development of such devices.

BeO ceramics are one of the most popular choices of structural materials in the nuclear energy industry due to their high thermal conductivity, high strength, high insulation capacity, chemical stability, and high temperature resistance. The volume expansion of BeO ceramics and the microcrack generation mechanism, as well as the design of ceramic structures, under irradiation conditions have been hot topics in research into structural materials suitable for nuclear energy generation. Maxim V. Zdorovets et al. [3] investigated the radiation-induced damage kinetics of beryllium oxide ceramics under low-energy helium ion irradiation. The irradiation-induced structural changes were found to be related to the amorphization process and the increase in the dislocation density of the ceramics. In addition, a decrease in the hardness and wear resistance of the ceramics was also found. These results undoubtedly have a positive significance for the in-depth study of the compositional and structural design of ceramics under irradiation conditions.

Anisotropic-shaped zirconia structures such as nano-rods, nano-belts, or platelets are thought to be useful starting materials for the oriented growth of zirconia ceramics and the fabrication of shape-dependent zirconia catalysts or catalytic supports, luminescent materials, gate dielectrics, and solid-state oxide fuel cells. Anisotropic ZrO₂ particles with octahedron-, diamond-, and plate-like morphologies were successfully synthesized through a facile hydrothermal treatment approach using NaBF4 as mineralizer by Ling Gao et al. [4]. The results showed that F- plays an essential role in tuning the crystallinity and size of primary ZrO₂ nanorods along the [001] direction. The secondary particles mainly crystallize on the small primary nanoparticles through the oriented attachment mechanism. In addition, octahedron-like ZrO₂ particles have the highest MB degradation rate. Clearly, these results hold positive significance for exploring the potential utilization of these structures as photocatalytic materials and starting materials for preparing oriented polycrystalline zirconia ceramics.

Al0.1CoCrFeNi high-entropy alloys have excellent mechanical properties which are superior to those of traditional alloys. However, finding a suitable strengthening mechanism is still challenging. The tensile properties of high-entropy alloys and the crack propagation mechanism have been investigated using the molecular dynamics method by Cuixia Liu et al. [5,6]. They thought that, during the plastic deformation of high-entropy alloys, each dislocation nucleates and emission continues near the crack tip, alongside the formation of complementary stacking layers or twins. Therefore, they argue that atomic shear behavior is caused by a dislocation motion. The above viewpoints provide a theoretical basis for improving the mechanical properties of high-entropy alloys.

Hafnium dioxide (HfO₂) boasts excellent optical, thermal, and mechanical properties and is one of the most important high-refractive-index oxide materials used for manufacturing interference multilayer films, and is also known to be a material with a high laser damage threshold (LIDT). Electron beam physical vapor deposition (EB-PVD) is considered to be one of the most critical techniques for preparing multilayer interference films; however, films prepared using this method tend to be porous, and segregation may occur during fabrication, leading to a decrease in the HfO₂ film’s resistance to laser damage. Yingxue Xi and colleagues [7] studied a series of ion beam processing methods, comparing the impact of argon ions and oxygen ions at different energies on the optical performance, laser damage resistance, and surface quality of the films. The study found that oxygen ions at certain energies can effectively increase the film’s laser damage threshold, primarily because oxygen ions can enhance the film’s density and adjust the composition of segregated elements within the film. This finding is of significant value for enriching the preparation of laser film thresholds and clarifying the factors associated with film thresholds.

Molybdenum oxides, a type of metal oxide with an n-type semiconducting and nontoxic nature, have attracted much attention due to their diverse functional applications in electronics, catalysis, sensors, energy-storage units, field emission devices, superconductor lubricants, thermal materials, biosystems, and chromogenic and electrochromic systems. A corresponding study about the sintering of MoO₂ micropowders was carried out by Jongbeom Lee et al. [8] The authors discussed the morphological transformation and grain size changes in MoO₂ micropowders under the sintering process, analyzed the corresponding physical mechanisms, and drew clear conclusions. This serves as a good reference, providing an in-depth explanation of the basic knowledge in this field. Another fundamental study by Daryn B. Borgekov [9] focuses on the field of alternative energy. He investigated the effect of a change in the lanthanum concentration (La) during the synthesis of perovskite-like ceramics based on strontium ferrite on phase formation and subsequent changes in the conductive and thermophysical parameters. The results show that impedance spectroscopy shows a significant increase in the permittivity of the synthetic ceramics as the concentration of lanthanum in the synthetic ceramics increases over a limited range; there is also an increase in the tangent of the dielectric loss at a defined frequency. Furthermore, the resistivity decreases by one order of magnitude.

Mohammed Sobhy [10] reported the design of a fundamental application of this technology. He proposed using piezoelectric and piezomagnetic materials for electromechanical energy and magnetic energy interconversion which can be applied in nanoelectromechanical systems such as heat exchangers, smart devices, nuclear devices, and nanogenerators. Based on a refined four-unknown shear deformation plate theory, the free vibration of piezoelectromagnetic plates reinforced with functionally graded graphene nanosheets (FG-GNSs) under simply supported conditions is analyzed. After a rigorous mathematical derivation and analysis, it was found that the elastic foundation stiffness, graphene weight fraction, applied magnetic potential, and electromagnetic properties of graphene enhance the plate stiffness, leading to a noticeable increment in the fundamental frequency. Conversely, the increase in the side-to-thickness ratio, plate aspect ratio, and applied electric potential weakened the plate strength; therefore, the frequency decreases. Such research can have positive value for continuing to optimize the system design subsequently.

3. Conclusions

This Special Issue contains a number of studies related to basic material design, semiconductor material applications, and the application and conversion of energy, as well as designs for functional devices, showing a wealth of research results and providing a platform for researchers to communicate with each other. As Guest Editors, we would like to thank all the authors for their contributions and efforts.