Editor-in-Chief Sean Shaheen reflects on the role of JPE in advancing critical technologies toward rapid realization of large-scale change in global energy systems.

We propose structures that are colored with photoluminescence materials for radiative cooling applications. Using simulations, we show that implementing photoluminescence materials provides color to the structures by shifting electromagnetic energy between spectrums. Resulting additional solar energy absorption due to coloration is lower with photoluminescence compared to the traditional materials used for spectrally selective absorption, such as pigments and nanosized metallic resonators. Thermal and visual performance of different types of photoluminescence materials such as phosphors and quantum dots are investigated. Effects of Stokes shift and quantum yield, which are the photoluminescence properties that characterize the energy shift between spectrums, are quantified.

We describe an algorithm to extract the complex refractive index of a material from broadband reflectance and transmittance measurements taken by spectrophotometers. The algorithm combines Kramers–Kronig analysis with an inversion of Fresnel’s equations to provide a direct method of solving for the refractive index which is accurate, even for weakly absorbing materials, and easily applicable to radiative heat transfer calculations. The algorithm is validated by extracting the complex refractive index of polydimethylsiloxane between 0.25  μm and 100  μm and comparing against existing literature. We also discuss the importance of broadband optical properties to passive radiative cooling and details of the uncertainty analysis of the algorithm.

In our work, UV-response with a small visible light absorption TiO₂ nanoparticles were supported on lamellar La₂NiO₄ perovskite to build a type I heterojunction for efficient hydrogen production under visible light. It was found that, with the increase of La₂NiO₄ contents, the hydrogen production rates gradually increased and amounted to the highest value when the mass fraction of La₂NiO₄ was 8 wt. %, which is 39.5 times that of the initial La₂NiO₄ nanosheets without the cocatalyst Pt. When 1 wt. % Pt was loaded, the photocatalytic activity for the composite photocatalyst increased by 369.0 times that of the initial La₂NiO₄. Our work should be of value for the preparation of visible responsive heterojunction photocatalysts with high activity, fair stability, and low toxicity.

The optical absorption and heat transfer properties of fluid can be improved by suspending nanoparticles in a base fluid. Due to the strong photothermal effect around nanoparticles, water around the particles evaporates when exposed to light. Therefore, nanofluids can be used as the working fluid of solar evaporation devices. The evaporation heat transfer model of the Ag nanofluid is established. The temperature distribution and vapor concentration distribution around nanofluids are simulated at low concentrated solar power. Effects of the particle size and volume concentration on the evaporation performance are analyzed. When the volume concentration is small (f_v  =  0.01  %  ), the effect of particle size on evaporation is obvious, and the evaporation increases with the increase of particle size. When the particle radius R increases from 5 to 40 nm, the evaporation amount increases 17.8% from 0.0286 to 0.0337 g. For the nanofluids with smaller particle sizes (R  <  20  nm), the evaporation tends to be stable with the increase of concentration, reaching about 0.0318 g. For the nanofluids with larger particle sizes (R  =  40  nm), the evaporation decreases significantly with the increased concentration. When the volume concentration increases from 0.01% to 0.1%, the evaporation decreases from 0.0337 to 0.0288 g. Therefore, the particle size and volume concentration should be considered comprehensively when choosing nanofluids as evaporation working fluids. When the volume concentration is >0.05  %  , the nanofluids with smaller particle sizes should be selected. We provide guidance for the utilization of nanofluids for solar evaporation.

The pattern of the front electrode and the solar cell size has a significant influence on the performance of solar cells. In order to improve the conversion efficiency of solar cells, we present a combined finite-element-genetic algorithm (GA) method for designing the front electrode and solar cell size. In the proposed method, a solar cell is considered to consist of many small unit cells, and these unit cells can well describe the current density and voltage distribution of the solar cell. In the GA, each individual represents a solar cell with a particular size and operates at a particular voltage. The validity of the proposed method is tested on the front electrode and solar cell size design problem of the side-contact and gridded cells. Two existing optimization methods are also used to optimize the front electrode and solar cell size of the two kinds of solar cells. Based on solar cells of different sizes, different optimization results are obtained using either of the two existing optimization methods. The unique optimization result can be obtained using the proposed method, and the optimization result is better than that obtained using the two existing optimization methods.

The gallium content-dependent theoretical limit of the efficiencies of Cu  (  In  ,  Ga  )  Se₂ solar cells were studied using a MATLAB model developed based on the Shockley–Queisser detailed balance. The developed model included the temperature dependence of the bandgap according to the gallium content. The original Shockley–Queisser detailed-balance and the developed model at the ASTM G173-03 AM1.5G solar irradiance were used to calculate the gallium content and solar cell temperature-dependent theoretical efficiency limits of a Cu  (  In_{1  −  x}Ga_x  )  Se₂-based solar cell. Due to the spectral distribution of the solar irradiance, there were two “peaks” of efficiency: one at values of x around 0.2 prevails at lower temperatures and the other at values of x around 0.6 higher at temperatures above 0°C. Consequently, there is a “pit” with a minimum at x of around 0.5. Values of x corresponding to these values are higher for the temperature-dependent bandgap model. The calculated relative difference between the ultimate efficiency limit and the theoretical efficiency at x  =  0.3 at 310 K is <1  %  .

Concentrating photovoltaic (CPV) systems require less area of the solar cell while achieving a high efficiency. One of the development factors in the CPV includes the irradiance uniformity over the solar cell. To overcome this issue, a parabolic trough-based optical design is proposed using two nonimaging secondary reflectors: reflective grooves and compound parabolic concentrator (CPC). The reflective grooves convert the line focus to a square shape irradiance distribution, and the CPC is used for redirecting the rays to the receiver. The proposed system delivers the concentrated light over the solar cell having a size of 30  ×  30  mm² at the center of the trough. The CPV system reduces the number of cells compared with conventional trough-based CPV systems by attaining the concentration ratio of 285. The results indicate that the system has achieved an optical efficiency of 60% at an acceptance angle of ±2  deg. The detailed optical design and raytracing simulation are presented showing that the proposed concentrator can achieve significantly higher overall concentration while maintaining irradiance uniformity.