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The high power conversion efficiencies of small-area perovskite solar cells (PSCs) have driven interest in the development of commercial devices. Rong et al. review recent progress in addressing stability, how to allow mass production, and how to maintain uniformity of large-area films. They note that lifetimes exceeding 10,000 hours under 1 sun (1 kW/m 2 ) illumination have been reported for printable triple mesoscopic PSCs. Science , this issue p. eaat8235 Perovskite solar cells (PSCs) have witnessed rapidly rising power conversion efficiencies, together with advances in stability and upscaling. Despite these advances, their limited stability and need to prove upscaling remain crucial hurdles on the path to commercialization. We summarize recent advances toward commercially viable PSCs and discuss challenges that remain. We expound the development of standardized protocols to distinguish intrinsic and extrinsic degradation factors in perovskites. We review accelerated aging tests in both cells and modules and discuss the prediction of lifetimes on the basis of degradation kinetics. Mature photovoltaic solutions, which have demonstrated excellent long-term stability in field applications, offer the perovskite community valuable insights into clearing the hurdles to commercialization.

Antimony selenide is an emerging promising thin film photovoltaic material thanks to its binary composition, suitable bandgap, high absorption coefficient, inert grain boundaries and earth-abundant constituents. However, current devices produced from rapid thermal evaporation strategy suffer from low-quality film and unsatisfactory performance. Herein, we develop a vapor transport deposition technique to fabricate antimony selenide films, a technique that enables continuous and low-cost manufacturing of cadmium telluride solar cells. We improve the crystallinity of antimony selenide films and then successfully produce superstrate cadmium sulfide/antimony selenide solar cells with a certified power conversion efficiency of 7.6%, a net 2% improvement over previous 5.6% record of the same device configuration. We analyze the deep defects in antimony selenide solar cells, and find that the density of the dominant deep defects is reduced by one order of magnitude using vapor transport deposition process. Antimony selenide possess several advantages for solar cell applications but state-of-the-art vapor transport deposition methods suffer from poor film quality. Here Wen et al. develop a fast and cheap method to reduce the defect density by 10 times and achieve a certified power conversion efficiency of 7.6%.

Cadmium telluride (CdTe) solar cells have attracted a lot of interest in recent years, attributed to their low cost and eco-friendly fabrication technique. However, the back contact is still the key issue for further improvement in device performance due to the work function difference between p-CdTe and metal contacts. In this study, the interatomic characteristics of zinc telluride (ZnTe) and Cu-doped ZnTe (ZnTe:Cu) as a back surface field (BSF) in CdTe structure is investigated using first-principles density functional theory (DFT) to overcome the Schottky barrier in CdTe solar cells. The incorporation of different doping levels of copper (Cu) in ZnTe on an atomic scale, where Zn 1− x Te:Cu x ( x  = 0, 2, 4, 6, 8, and 10) as the potential back surface field layers is investigated. The effect of doping concentration on electrical characteristics such as bandgap structure and density of states (DOS) were examined via ab initio with the Hubbard U (DFT + U) correction. The results showed an interesting gradual decrease in the bandgap energy of ZnTe from 2.24 eV to 2.10 eV, 1.98 eV, 1.92 eV, 1.88 eV, and 1.87 eV for the incremented value of Cu content of 3.13%, 6.25%, 9.38%, 12.50%, and 15.63%, respectively. Accordingly, it has been found that controlling of the effective copper doping, i.e., concentration, is crucial for developing efficient back contact junctions for high-efficiency CdTe thin-film solar cells.

The cadmium mercury telluride solid solution is one of the most important infrared photoelectronic materials in the world. In obtaining this compound, molecular beam epitaxy has a number of advantages over other methods. At the same time, this solid solution is quite demanding on the pre-growth processing of substrates. In this study, the polishing processes are the primary development in mastering the production of cadmium mercury telluride (211) wafers. A roughness value of ~1 nm is obtained.

Semiconductor x-ray detectors are widely used in experiments at synchrotron facilities. The performance of these detectors depends heavily on the semiconductor material properties. Improvements in crystal growth and device processing are key to developing “high-Z” (high atomic number) semiconductors for hard x-ray detection. Germanium is the most mature high-Z semiconductor and is widely used in x-ray detectors, but it has the drawback of needing to be cooled during operation, often to cryogenic temperatures. Compound semiconductors with wide bandgaps can be used at room temperature, but crystal defects can degrade their performance. Gallium arsenide currently shows poorer energy resolution, but its comparative robustness and stability over time make it a strong option for imaging detectors. Cadmium telluride and cadmium zinc telluride both provide higher detection efficiencies at extreme x-ray energies as well as good energy resolution; the main challenge with these materials is maintaining consistent behavior under a high x-ray flux.

Liquid-phase epitaxy (LPE) is a material growth technology used in the fabrication of mercury cadmium telluride (HgCdTe) infrared (IR) detectors, which is the highest-performing solution in the IR community. This paper presents the most successful LPE technology, “infinite-melt” vertical liquid-phase epitaxy (VLPE) from Hg-rich solutions. To fulfill requirements for large-format infrared focal-plane detectors, solutions were required to improve the uniformity, yield, and material properties of HgCdTe liquid-phase epitaxial (LPE) and cadmium zinc telluride (CdZnTe or CZT) bulk growth as well as substrate fabrication processing. Raytheon Vision Systems (RVS) produces CdZnTe substrates for epitaxial growth, and in this work, advancements in boule growth processes and metrology led to the identification and elimination of the infrared opaque extended defects within CdZnTe material. Boule growth advancements have also decreased the Cd precipitate defect diameter by a factor of 4. These improvements enabled large-format focal-plane arrays (FPAs) with uniform sensor response. Also, improvement in our polishing process has reduced substrate processing time and total thickness variation (TTV), improving downstream lithography and hybridization processes. Optimizing LPE growth chemistry dynamics resulted in the elimination of large defects, decreased density of epitaxial defects, and improved control of cut-on and thickness of resulting layers. Implementation of custom software allowed real-time prediction during layer growth which resulted in a higher process yield. The continuous improvement of VLPE results in better uniformity, reduced noise, and competitive die size, compared to other long-wave (LW) second-generation detector processes.

Positron Emission Tomography (PET) is a widely-used imaging modality for medical research and clinical diagnosis. Imaging of the radiotracer is obtained from the detected hit positions of the two positron annihilation photons in a detector array. The image is degraded by backgrounds from random coincidences and in-patient scatter events which require correction. In addition to the geometric information, the two annihilation photons are predicted to be produced in a quantum-entangled state, resulting in enhanced correlations between their subsequent interaction processes. To explore this, the predicted entanglement in linear polarisation for the two photons was incorporated into a simulation and tested by comparison with experimental data from a cadmium zinc telluride (CZT) PET demonstrator apparatus. Adapted apparati also enabled correlation measurements where one of the photons had undergone a prior scatter process. We show that the entangled simulation describes the measured correlations and, through simulation of a larger preclinical PET scanner, illustrate a simple method to quantify and remove the unwanted backgrounds in PET using the quantum entanglement information alone. Gamma photons used in positron emission tomography are predicted to be produced in an entangled state. Here, the authors simulate the effects of entanglement and test them through comparison with experimental data from a PET demonstrator apparatus, showing the potential gains in background suppression.

The highly reactive nature of reactive oxygen species (ROS) is the basis for widespread use in environmental and health-related fields. Conventionally, there are only two kinds of catalysts used for ROS generation: photocatalysts and piezocatalysts. However, their usage has been limited due to various environmental and physical factors. To address this problem, herein, we report thermoelectric materials, such as Bi 2 Te 3 , Sb 2 Te 3 , and PbTe, as thermocatalysts which can produce hydrogen peroxide (H 2 O 2 ) under a small surrounding temperature difference. Being the most prevalent environmental factors in daily life, temperature and related thermal effects have tremendous potential for practical applications. To increase the practicality in everyday life, bismuth telluride nanoplates (Bi 2 Te 3 NPs), serving as an efficient thermocatalyst, are coated on a carbon fiber fabric (Bi 2 Te 3 @CFF) to develop a thermocatalytic filter with antibacterial function. Temperature difference induced H 2 O 2 generation by thermocatalysts results in the oxidative damage of bacteria, which makes thermocatalysts highly promising for disinfection applications. Antibacterial activity as high as 95% is achieved only by the treatment of low-temperature difference cycles. The current work highlights the horizon-shifting impacts of thermoelectric materials for real-time purification and antibacterial applications. Temperature difference induced H 2 O 2 generation by thermoelectric materials is an attractive strategy for environmental remediation purposes. Here the authors demonstrate Bi 2 Te 3 nanoplates based antibacterial filter as an effective candidate for indoor disinfection applications.

A topological insulator has surface metallic states that are topologically protected by time-reversal symmetry. Tin telluride is now shown to be a ‘topological crystalline insulator’, in which the surface metallic state is instead protected by the mirror symmetry of the crystal. A topological insulator is an unusual quantum state of matter, characterized by the appearance, at its edges or on its surface, of a gapless metallic state that is protected by time-reversal symmetry 1 , 2 . The discovery of topological insulators has stimulated the search for other topological states protected by other symmetries 3 , 4 , 5 , 6 , 7 , such as the recently predicted 8 topological crystalline insulator (TCI) in which the metallic surface states are protected by the mirror symmetry of the crystal. Here we present experimental evidence for the TCI phase in tin telluride (SnTe), which has been predicted to be a TCI (ref.  9 ). Our angle-resolved photoemission spectra show the signature of a metallic Dirac-cone surface band, with its Dirac point slightly away from the edge of the surface Brillouin zone in SnTe. Such a gapless surface state is absent in a cousin material, lead telluride, in line with the theoretical prediction.

The interest in mid-infrared technologies surrounds plenty of important optoelectronic applications ranging from optical communications, biomedical imaging to night vision cameras, and so on. Although narrow bandgap semiconductors, such as Mercury Cadmium Telluride and Indium Antimonide, and quantum superlattices based on inter-subband transitions in wide bandgap semiconductors, have been employed for mid-infrared applications, it remains a daunting challenge to search for other materials that possess suitable bandgaps in this wavelength range. Here, we demonstrate experimentally for the first time that two-dimensional (2D) atomically thin PtSe 2 has a variable bandgap in the mid-infrared via layer and defect engineering. Here, we show that bilayer PtSe 2 combined with defects modulation possesses strong light absorption in the mid-infrared region, and we realize a mid-infrared photoconductive detector operating in a broadband mid-infrared range. Our results pave the way for atomically thin 2D noble metal dichalcogenides to be employed in high-performance mid-infrared optoelectronic devices. The mid-infrared technologies are essential to various applications but suffer from limited materials with suitable bandgap. Here the authors demonstrate that two-dimensional atomically thin PtSe 2 with variable bandgaps in the mid-infrared via layer and defect engineering is highly promising for mid-infrared optoelectronics.