Photovoltaic module performance in the field is strongly dependent on the optical properties of its component layers and the temperature dependencies of these properties. However, despite their importance, the temperature dependencies of the optical properties of many photovoltaic module components appear to have not been characterised. Hence, the assumptions regarding their optical stabilities at various temperatures have not been verified. In this study, a temperature-dependent spectrophotometry method is developed to enable this verification. The temperature dependencies of the optical properties of silicon nitride, ethylene vinyl acetate (EVA), and backsheets are characterised, and their impacts on module operations are quantified via ray-tracing simulations. It is concluded that (1) silicon nitride anti-reflection coatings are optically stable between room temperature and 85 degrees C, and (2) several temperature dependencies exist at different wavelengths in both EVA and backsheets, however, they do not have a significant impact on the module operation.

Efficient photocatalysts for water remediation require precise control of defects and phase composition, yet quantitative links between dopant level, polymorph evolution, defect chemistry, and photocatalytic activity remain incomplete. Herein, wafer‐scale combinatorial chemical beam vapor deposition is used to fabricate 6‐inch Nb x Ti 1−x O 2 wafers with a lateral niobium gradient ( x = 0.04–0.08), enabling spatially resolved mapping of structure–property relationships. Increasing Nb drives a progressive anatase‐to‐rutile transformation, with the rutile fraction rising from 2% to 49% across the wafer. Concurrently, Nb 5+ donor incorporation generates charge‐compensating Ti 3+ states and oxygen vacancies, which modulate the electronic structure and suppress carrier recombination. Photocatalytic benchmarking using methylene blue as a model probe reaction reveals a fivefold rate enhancement at the highest Nb level, establishing a direct correlation between dopant concentration, phase formation, defect chemistry, and photocatalytic performance. Importantly, the wafers exhibit operational stability and reusability over repeated cycles, retaining activity with minimal loss upon repeated use. These results establish a transferable phase–defect–activity framework and highlight Nb doping, combined with wafer‐scale combinatorial synthesis, as an effective strategy for designing durable TiO 2 ‐based photocatalysts for sustainable water treatment.

Understanding and controlling dopant activation and parasitic absorption in polycrystalline silicon (poly-Si) passivating contacts is critical for enhancing the efficiency of tunnel oxide passivating contact (TOPCon) solar cells. In this work, we systematically investigate the effects of carbon incorporation into plasma-enhanced chemical vapour deposited (PECVD) n (+) poly-Si films, and establish a comprehensive correlation between nanoscale morphology, dopant activation, optical properties, and passivation performance. By tuning methane gas flow during deposition, we demonstrate that carbon incorporation suppresses film crystallization, modulates dopant activation, and alters free carrier absorption via changes in effective mass and local microstructure. Advanced characterization techniques, including spectroscopic ellipsometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), conductive-AFM, and Kelvin probe force microscopy (KPFM), reveal that Si-C bonding and reduced grain size lead to lower work function, and enhanced chemical passivation. Optical simulations confirm a reduction in parasitic absorption by similar to 0.1 mA/cm(2) per 100 nm at the rear surface, while lifetime measurements exhibit an implied open-circuit voltage of 747.6 mV and a carrier lifetime of 6.7 ms, among the highest reported values for poly-Si passivating contacts. These findings provide new mechanistic insights into carbon-engineered poly-Si layers and highlight their potential for integration into high-efficiency TOPCon and back-contact silicon solar cells.

Currently, single-layer antireflection coated (SLARC) solar glass has a dominant market share of 95% compared to glass with other coatings or no coating, for Si PV modules. This antireflection coating (ARC) results in an efficiency gain of 2-3%. However, there are issues with these SLARCs: (1) solar cell warming due to increased sub-bandgap light absorption (by +0.4 similar to 1.2 K), counteracting the cell current gain and accelerating the aging of the solar panels, and (2) poor durability due to the coating's porous structure (typically lasting <= 5 years). This paper aims to develop a non-porous multilayer coating (MLC) that is more durable and will act as a spectrally selective filter for solar modules. Studies have been conducted on MLCs in terms of optical, microstructure, mechanical, and durability properties compared with commercial single-layer AR coatings. The MLCs showed superior performance in durability and benefit in reducing parasitic heat absorption in the non-usable wavelength range. Also, a techno-economic analysis model based on the multifunctional coating specifically to evaluate economic benefits has been developed.

Reducing the operation temperature of photovoltaic (PV) modules will allow prolonging their service time and energy output. This work investigated a passive PV module cooling technique by attaching vortex generators (VGs) on the rear surface of PV modules. The rectangular wing VGs of size 2 x 3 cm, are made from aluminium sheet (Al VG) or 3D printed thermally conductive polymer (Poly VG). After ten months of data collection on an open rack system, we have gained insight into the wind speed- and direction-dependent performance of the Al and Poly VGs. The pronounced difference in thermal conductivity of the two materials helps distinguish cooling due to vortex generation, predominant at low wind speeds, from the heat sink effect, prevalent at higher wind speeds. Despite being optimised for free convection, both VGs demonstrated 1.5 degrees C of cooling under low wind and high irradiance, while Al VGs provided 2.5 degrees C of cooling under high module temperature and windy scenarios. Both VGs exhibit equivalent performance with south and west winds, indicating the dominance of the vortex generation mechanism. The module equipped with VGs exhibited an increase in convective heat transfer coefficient as evaluated by the thermal balance model.

The antireflection(AR) coating applied to solar glass in photovoltaic modules has remained largely unchanged for decades, despite its well-documented lack of durability. Traditional porous structured single-layer AR coatings last as little as 5 years in the field. In this paper, we propose a novel 5-layer dense AR coating design that offers improved durability and effectiveness compared to traditional coatings. This paper provides detailed insights into the development and characterization of the novel 5-layer AR coating, providing guidance to the photovoltaic community seeking to improve the efficiency and longevity of solar modules.

The antireflection (AR) coating applied to solar glass in photovoltaic modules has remained largely unchanged for decades, despite its well-documented lack of durability. Traditional porous structured single-layer AR coatings last as little as 5 years in the field. In this paper, we propose a novel five-layer dense AR coating design that offers improved durability and effectiveness compared to traditional coatings. This paper provides detailed insights into the development and characterization of the novel five-layer AR coating, including simulation, optical measurements, and abrasion testing, providing guidance to the photovoltaic community seeking to improve the efficiency and longevity of solar modules.

The reversal of halide ions is studied under various conditions. However, the underlying mechanism of heat-induced reversal remains unclear. This work finds that dynamic disorder-induced localization of self-trapped polarons and thermal disorder-induced strain (TDIS) can be co-acting drivers of reverse segregation. Localization of polarons results in an order of magnitude decrease in excess carrier density (polaron population), causing a reduced impact of the light-induced strain (LIS - responsible for segregation) on the perovskite framework. Meanwhile, exposing the lattice to TDIS exceeding the LIS can eliminate the photoexcitation-induced strain gradient, as thermal fluctuations of the lattice can mask the LIS strain. Under continuous 0.1 W cm⁻2 illumination (upon segregation), the strain disorder is estimated to be 0.14%, while at 80 °C under dark conditions, the strain is 0.23%. However, in situ heating of the segregated film to 80 °C under continuous illumination (upon reversal) increases the total strain disorder to 0.25%, where TDIS is likely to have a dominant contribution. Therefore, the contribution of entropy to the system's free energy is likely to dominate, respectively. Various temperature-dependent in situ measurements and simulations further support the results. These findings highlight the importance of strain homogenization for designing stable perovskites under real-world operating conditions.

A proof-of-principle double-layer symmetrical supercapacitor with nanoporous copper/copper oxide electrodes and an aqueous electrolyte is investigated. The electrodes are manufactured by selective dissolution of Al from a eutectic composition of Cu 17.5 Al 82.5 using 5 M NaOH. The ostensible (i.e., net external) capacitance of a symmetrical two-electrode cell with 0.1 M KNO 3 electrolyte is assessed over a series of charge/discharge cycles and is about 2 F per gram of Cu in this simple prototype. Capacitance varies during a discharge cycle due evidently to the deeply buried surfaces and pseudocapacitive reactions contributing charge toward the end of a discharge cycle. In principle such a device should have very low ohmic losses due to its highly conductive backbone and would be suitable for applications requiring maximum energy efficiency over repeated cycling. The aqueous electrolyte ensures fire safety but this comes at the cost of lower energy content. Graphical abstract

The unexpected growth of highly aligned and optically polarizing metallic fins during physical vapor deposition under modestly oblique conditions is investigated. The fins exhibit nanoscale dimensions and are formed when Al is co-sputtered with any of V, Cr, Nb, Mo, Ta, W, Ru, Fe, Ni, Pt, Zr, Mg, and Ti. It is proposed that the phenomenon is caused by anomalously low atomic mobility in the alloys and intermetallic compounds formed by co-depositing with Al. In contrast, when Cu, Ag, and Au (which diffuse more rapidly in Al) are deposited, no fins form. There is a sharp visible transition in optical properties as the ratio of Al to other element is decreased: the color of the sample changes from black to silver-white for compositions containing less than about 55 atom % Al. The region over which the color change occurs is associated with a very strongly polarized reflectance. Cross-sectional elemental mapping and Monte Carlo simulations suggest that growth of the fins may be nucleated by Al hillocks and enhanced by shadowing effects. The diversity of suitable metals makes this a versatile technique for producing nanoscale polarizing surfaces suitable for high-flux and high-temperature applications.

Photons excited into ground state modes at finite temperature display partitioning among photon phases, lifetimes and distances travelled since creation. These distributions set the distance from an interface a created photon has some chance of emission. Excited photons have phase velocity set by their mode’s propagation index n which sets mode density then internal energy contribution. All photons that strike an interface obliquely if emitted are refracted, and their exit intensities are irreversible except when weak internal attenuation occurs. Attenuation index k near zero degrees is small, so reversibility is approximate. As temperature rises refraction of exiting photons varies. Total emission remains reversible after transitioning through a nonequilibrium state with no other heat inputs. In equilibrium the densities of excitations that create and annihilate photons are in balance with photon densities, and emissivity dependent on n, k, temperature, and internal incident direction. Exit intensities from pure water and crystalline silica are modelled. They contain strong resonant intensities, and match data accurately. Intrinsic resonances formed within liquids and compounds are due to photon modes hybridising with localized excitations, including molecular oscillations and the anharmonic component of lattice distortions. They explain the many resonant spectral intensities seen in remote sensing. Each hybrid oscillator is a photonic virtual bound state whose energy fluctuates between levels separated by hf. Other features addressed are radiance when solid angle changes at exit, anomalous refraction, thermal recycling of internally reflected photons, fluxes within multilayers, and enhanced internal heat flux from phonon drag by photon density gradients under an external temperature gradient.

We demonstrate switchable polarized thermal emission from VO2 nanofin stacks fabricated by co-deposition, etching, and oxidation. We find that reverse switching of the thermal emission is enabled by a reflecting underlayer and induced by either short oxidation time or additional deposition of a reflecting underlayer. Observed thermal emission is well explained by a biaxial Bruggeman effective medium model, which predicts the strong polarization change for aligned fin layers in the micron thickness range. The dominant polarization of the emission is modulated by the presence of a reflector, oxidation of the fins, fin fill-factor, and structural anisotropy. Normal incidence polarized emittance change of up to 0.6 is theoretically possible, and we were able to demonstrate a change of 0.34, similar to that predicted by the model. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

The Stefan-Boltzmann constant arose from photon densities inside a cavity, but inside matter photon mode densities are material specific. Photon speeds are governed by the mode they occupy, so mode densities can be expressed in terms of speed. Cavity intensities at temperature T_K combined [8π k^4/c^3h^3] T_K ^4 with (π^4/15). A material dependent number from summation of internal photon spectral energy densities replaces π^4/15. Spectral densities are presented for water, germanium and silver. Output intensity combines revised hemispherical emittance ϵ_Q,H based on these densities, with universal factor [8π k^4/c^3h^3] T_K ^4. Emitted radiance after interface internal reflectance of directionally invariant internal radiance elements defines ϵ_Q,H. Predicted internal densities are verifiable using measured external spectral intensities, provided refraction upon exit is accounted for in emissivity, which the Kirchhoff rule neglects. Virtual bound state photon resonances are predicted in dielectrics and observed.

An iterative algorithm is used to design a spectrally selective thin‐film stack to provide maximum solar‐to‐thermal conversion efficiency at the very high operating temperatures associated with high solar concentrations. The resulting stack is then fabricated by magnetron sputtering and characterized. It is composed of two Ta:SiO2 layers with differing Ta nanoparticle contents on a refractory metal substrate. A SiO2 antireflecting overlayer completes the stack. Optical and microstructural characterizations indicate that the stack achieves 97.6% solar absorptance up to 900 °C. Spectral selectivity and thermal stability improve on annealing in two ways, first, due to recrystallization of Pt or Ta back reflectors which lowers room temperature thermal emittance to 0.15 from 0.18, and to 0.14 from 0.21, respectively; and second, due to alloying of substrate atoms with the Ta nanoparticles of the cermet.

Metal–oxide–metal devices based on amorphous VOx are shown to exhibit one of two distinct negative differential resistance (NDR) characteristics depending on the maximum current employed for electroforming. For low compliance currents they exhibit a smooth S-type characteristic and have a temperature-dependent device resistance characterized by an activation energy of 0.25 eV, consistent with conduction in polycrystalline VO2, while for high compliance currents they exhibit an abrupt snap-back characteristic and a resistance characterized by an activation energy of 0.025 eV, consistent with conduction in oxygen deficient VOx. In both cases, the temperature dependence of the switching voltage implies that the conductivity change is due to the insulator–metal transition in VO2. From this analysis, it is concluded that electroforming at low currents creates a conductive filament comprised largely of polycrystalline VO2, while electroforming at high currents creates a composite structure comprised of VO2 and a conductive halo of oxygen deficient VOx. The effect of electroforming on the NDR mode is then explained with reference to a lumped element model of filamentary conduction that includes the effect of a parallel resistance created by the halo. These results provide new insight into the NDR response of vanadium-oxide-based devices and a basis for designing devices with specific characteristics.

PbS quantum dot solar cells (QDSCs) have emerged as a promising low-cost, solution-processable solar energy harvesting device and demonstrated good air stability and potential for large-scale commercial implementation. PbS QDSCs achieved a record certified efficiency of 12% in 2018 by utilizing an n+-n-p device structure. However, the p-type layer has generally suffered from low carrier mobility due to the organic ligand 1,2-ethanedithiol (EDT) that is used to modify the quantum dot (QD) surface. The low carrier mobility of EDT naturally limits the device thickness as the carrier diffusion length is limited by the low mobility. Herein, we improve the properties of the p-type layer through a two-step hybrid organic ligand treatment. By treating the p-type layer with two types of ligands, 3-mercaptopropionic acid (MPA) and EDT, the PbS QD surface was passivated by a combination of the two ligands, resulting in an overall improvement in open-circuit voltage, fill factor, and current density, leading to an improvement in the cell efficiency from 7.0 to 10.4% for the champion device. This achievement was a result of the improved QD passivation and a reduction in the interdot distance, improving charge transport through the p-type PbS quantum dot film.

Spectrally-selective solar absorbing coatings based on the Ti1-xAlxN system were deposited using DC magnetron sputtering. Due to their refractory nature and very suitable optical properties, these were considered for high temperature solar thermal energy conversion. The composition of Ti1-xAlxN, (effectively, the Ti/Al ratio) was optimized to achieve a maximized solar absorptance. The optimum composition was then tested in a tandem absorber which included anti-reflective layers. A stainless steel substrate was used in order to simulate service in parabolic trough-based power plants that use stainless steel pipe to carry the heat-transfer fluid. High temperature annealing of the stack caused structural modifications but the solar absorptance of 92% was retained even after annealing at 900 °C.

The dielectric function of the intermetallic compound PtAl2 is assessed and found to be comparable to that of titanium nitride, suggesting that nanostructures of PtAl2 may be suitable for plasmonic devices. In order to probe this further, the optical properties of experimentally produced arrays of nanoscale PtAl2 semi-shells of about 300 nm diameter were examined and compared to the results of numerical simulations. The structures showed a broad localized surface plasmon resonance centered on similar to 1.3 eV (similar to 950 nm), which matched the simulations. Calculations showed that a ten-fold enhancement of the electric field of the incident light will be achieved around the rim of suitably oriented PtAl2 semi-shells. The phase of the oscillation induced by 1060 nm light will be retarded by pi/2 relative to the incident light. This is indicative of a resonant condition. These observations suggest that it could be worthwhile to investigate possible applications for this and other intermetallic compounds in nanoscale plasmonic devices.

Here we present our recent developments in temperature dependent ellipsometry, FTIR and emittance measurements of flat and structured vanadium dioxide (VO2) surfaces allowing significant control of switchable radiative cooling beyond that attainable via traditional VO2 surfaces. VO2 undergoes a metal-insulator transition at a critical temperature of ~ 68°C; previous work has investigated tuning of this critical temperature over a wide range of temperatures. Here we exploit the shift in optical properties to produce surfaces with various emittance temperature profiles that modulate the thermal radiative transfer to/from a surface. Designing surfaces with different temperature emittance profiles requires accurate optical/thermal characterisation of materials. VO2 is produced by sputtering of vanadium followed by post deposition annealing in a 0.1Torr to 0.3Torr Air atmosphere at 450°C to 550°C, in-situ optical monitoring allows for accurate termination of the annealing process once the desired optical response is achieved.

Traditional polymer polarizers degrade in harsh environments and at high temperatures, reducing the polarization effect. In contrast, polarizers produced with refractory metals have vastly improved thermal stability and resistance to harsh environments but are expensive to fabricate. Here we demonstrate prototype refractory metal wire grid polarizers produced by co-sputtering molybdenum and aluminum under specific conditions. Removal of the aluminum through selective dissolution enables the nanostructure array to transmit light. The polarization spans 500-1100 nm and the extinction ratio significantly increases to > 100. Possessing broadband polarization and sufficient extinction ratios, the new polarizing film has potential applications in coatings for sunglasses, windows, pyrometers, scientific instruments, and LCD panels.