Editor in Chief Sean Shaheen presents a revised list of interest areas within the Scope of the Journal of Photonics for Energy.

Guest editors Aaswath Raman, Xiaobo Yin, and Peter Bermel introduce the Special Series on Radiative Cooling.

Radiative cooling as a spontaneous cooling phenomenon without any energy input has great research value and broad application prospects. However, environmental shields around the thermal emitter have a negative impact on the radiative cooling power of thermal emitters. A PTFE-Al was used as the radiative cooling thermal emitter, and the radiative cooling performances with different unilateral shielding angle were measured. The temperature difference of 7.4°C was achieved in an open and unobstructed environment, while the temperature difference of 2.8°C at the unilateral shielding angle of 90 deg. Furthermore, using the energy conservation model, we theoretically calculated the radiative cooling powers and the temperature differences of the thermal emitter under different shielding conditions, which were in good agreement with the experimental results.

Passive radiative cooling provides an energy-saving method for heat management in buildings. Solar reflective paints are versatile and scalable formats that can be readily applied for this cooling technology. We investigate solar reflective paints consisting of hollow silica (SiO₂) and hollow titanium dioxide (TiO₂) microparticles as pigments and methyltrimethoxysilane as a binder. The hollow microparticles are synthesized via sol-gel and etching methods to control their diameter. Paint formulation is optimized for high total solar reflectance, measured by a UV-visible-near infrared photospectrometer, without exceeding the critical particle volume content. By introducing air volume into the particles and selecting optimal particle size, solar reflectance of the dry paints is significantly improved. Compared to TiO₂ microparticle samples, paints with hollow SiO₂ microparticles are more effective at rejecting solar irradiation on average while also requiring less particle volume content. Thermal and spectral emissivity measurement also indicates that the hollow SiO₂ microparticle paint has the highest broadband infrared emission, followed by a commercial paint and a TiO₂ sample. Outdoor experiment in a tropical climate demonstrates that the paint with hollow SiO₂ microparticles has better cooling performance than a commercial cooling paint product. The results suggest the potential of hollow SiO₂ microparticles for improving radiative cooling paints.

To reduce costs, the solar cell industry aims at producing thinner solar cells. Structuring the surfaces of optically thin devices is important for avoiding transmission-related losses and, hence, increasing their efficiency. Light trapping leads to longer optical pathlengths and increased absorption of energy. In addition, resonances in the nanostructures enhance the absorption in the energy-converting material. Further, resonances in periodic structures may couple with each other and thereby increase the absorption. Here, we establish a model system consisting of a multilayered solar cell to study resonances and coupling of resonances in a one-dimensional system. We show that resonances in energy-converting and nonenergy converting layers exist, evaluate the resonances and the coupling of resonances in different thin-film systems, and show how they affect the total absorption of energy in the energy-converting layer. We optimize the parameters of the multilayered thin-film systems to achieve an increase in the amount of the absorbed energy. We find that resonances in nonabsorbing material at the top may lead to absorption enhancement, while we cannot find any enhancement effect due to the coupling of resonances.

Ultraviolet fluorescence (UVF) imaging is a widely used technique to analyze encapsulant discoloration, which is one of the prominent degradation modes in photovoltaic (PV) modules. Conventionally, UVF is done during nighttime or in a dark room, but performing UVF imaging during nighttime causes several inconveniences including safety due to snakes and other animals and inconvenient scheduling issues for the plant owners. Similarly, performing UVF imaging indoors requires dismounting the modules from the racks and moving them to the laboratory, which are labor-intensive and time-consuming tasks and could damage the module or may cause the energy loss due to partial/complete plant/array shutdown. Moreover, the manufacturer/installer warranty may be voided if the modules are removed from the racks. An outdoor UVF setup that can be used during the daylight can be a better alternative to the indoor or nighttime setup, provided it ensures there is no leakage of ambient light into the covered testing structure. We propose a unique, portable, and user-friendly outdoor UVF setup design that can tackle the issue of the ambient light leaking in, give uniform UV light, and provide enough room to accommodate the UV light source and camera to capture module images. We also classify the encapsulant discoloration into three classes depending on the discoloration intensity level. Furthermore, using the image processing technique, the percentage of browning was calculated in each cell/module.

Reducing the surface optical loss and broadening the spectral response range can improve the power conversion efficiency (PCE) of the tandem solar cell (TSC). In this study, SiO₂  /  MgF₂  /  SiO₂  /  MgF₂ four antireflective coatings (ARCs) on top of perovskite/silicon TSC were designed, and the influence of each layer on the TSC performance was simulated and analyzed. The results indicate that the four ARCs enhanced light absorption over the 380- to 1200-nm wavelength range, and increased the PCE of the TSC from 20.79% to 24.16%, a 16.21% rate of increase. For cost savings, the four ARCs were re-optimized; the PCE of the TSC was improved to 23.6%.

Solar-driven CO₂ reduction to solar fuel is an effective way to deal with the greenhouse effect and energy crisis. A one-step hydrothermal method was used to synthesize Bi₄Ti₃O₁₂  /  SrTiO₃ composite photocatalysts. The heterogeneous structure formed by intimate contact was observed between SrTiO₃ (STO) nanoparticles and Bi₄Ti₃O₁₂ (BTO) nanoplates, achieving an enhanced photocatalytic CO₂ reduction yield of CO (13.37  μmol  /  g) that was 5.74-fold that of pure STO (2.33  μmol  /  g), with a high yield of CH₄ (1.55  μmol  /  g). Characterizations of phase composition, morphology, and optical/electrochemical properties were applied to prove the heterojunction structure and its role in improving the photocatalytic performance. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy tests demonstrate that electrons transfer from STO to BTO and result in the generation of an internal electron field between the two phases. Consequently, a direct Z-scheme system was formed: photoelectrons in the conduction band of BTO transferred to the valence band of STO to recombine with the holes thus spatially separated the photogenerated electron–hole pairs while enabling the photocatalyst to achieve the maximum reduction and oxidation capability. The catalyst structure system proposed here may bring new ideas for the development of titanate-based photocatalysts with high CO₂ reduction activity.

Structured surfaces are used to reduce reflection and enhance light-trapping in silicon solar cells. In this simulation study, we investigated the relationship between the refractive index of front-side coupling structures on top of planar wafer-based crystalline silicon solar cells and the light-trapping performance of the structures. A crossed diffraction grating with a period of 1  μm and random pyramid structures with varying refractive indices were considered. Simulations were carried out both at the cell level and at the complete module stack level. It is shown that the single pass light path enhancement factor (LPEF) only provides a rough estimate of the light-trapping properties. The light-trapping behavior can only be reliably assessed in the complete system level and these results deviate from the estimated single pass LPEF. It can also be shown that the refractive index of the structure strongly influences the light-trapping behavior.

Conventional photovoltaic (PV) modules (exclude interdigitated back contact modules) with silicon or gallium arsenide PV cells often have significant inactive module surface area. This results from wafer cutting techniques and metal contacts that reduce the module’s collection area and the resultant power conversion efficiency. A holographic light collector (HLC) combining a low-cost holographic optical element and a diffuser into conventional PV modules is proposed and evaluated to collect the solar illumination over the inactive module area. The angular tolerance and extra annual energy yield (EY) of the HLC are analyzed. It is found that improvements in EY of 4.5%, 4.1%, and 3.8% can be obtained when PV panels are deployed with two-axis tracking systems, single-axis tracking systems, and without tracking systems, respectively.

Semi-transparent luminescent solar concentrators window panels based on methylammonium lead bromide perovskite coatings are fabricated. It is shown that spraying as a large-scale fabrication technique delivers samples with comparable characteristics with those prepared by the physical vapor deposition or spin-coating methods. Three mirrorless, mirrored, and gaped-mirror configurations are designed for the current–voltage evaluation of the samples. According to our results, perovskite coating of glass slides with different film thickness leads to a 16% to 45% increase in the output electrical power. A gaped-mirror arrangement, through separating the bottom mirror in these devices, is introduced to mimic a typical double-glazed window panel for increasing the output efficiency. Moreover, it is demonstrated that fabricated luminescent concentrators can perform under different directional placements, which promises their widespread application in greenhouses and electrical vehicles.