The Journal of Photonics for Energy thanks the individuals who served as reviewers in 2018.

One advantage of microconcentrator photovoltaics (μ-CPV) is the range of possible circuit connection arrangements. Large numbers of cells can be connected in combinations of series and parallel strings, which can provide a means to protect the module against performance loss due to cell failure, cell shading, and other variations in cell parameters that may arise during the fabrication and wiring processes. We introduce a model to evaluate the best strategy for optimizing module reliability through circuit layout using a combination of series and parallel connected cell strings. The model uses realistic solar cell device parameters in an electrical network simulation, coupled with a Monte Carlo method to introduce defects into the array with different probabilities. We use the model to optimize the layout of a μ-CPV panel designed to be integrated with the conventional 60-cell crystalline silicon panels for diffuse light capture to produce a hybrid direct/diffuse CPV product.

The model of a graphene/n-type silicon (n-Si) Schottky near-field thermophotovoltaic cell (GSNTC) composed of an emitter and a photovoltaic (PV) cell is updated and investigated, in which the PV cell consists of a monolayer graphene and n-Si. Based on the recently modified thermionic emission for graphene, the formula for dark current density is rewritten. Formulas for the power and efficiency of the GSNTC are derived using the fluctuating electrodynamics. The general and optimum performances of the GSNTC are investigated. The optimization criteria of the key parameters are determined. Further, the effects of the vacuum gap and the emitter temperature on the optimum performance of the GSNTC are discussed. Our findings may provide guidance for developing high-efficiency near-field energy converters.

We numerically investigate the near-field radiative heat transfer (NFRHT) between magneto-optical GaAs nanowires using both the local effective medium theory and fluctuational dissipation theorem. Under the action of magnetic field, the atoms or ions within magneto-optical materials will produce magnetic induction phenomenon, resulting in the orderly arrangement of the magnetic moment in NFRHT, which have not been paid enough attention. NFRHT between two aligned GaAs nanowires and plates under different magnetic field intensities is demonstrated, in which the Lorentz–Drude equations of dielectric constant tensor are proposed to describe the dielectric constant as a magnetic field applied on the GaAs nanowires. Moreover, we evaluate the near-field radiation between GaAs nanowires/plates with different filling ratios and gap distance under extent magnetic field. Furthermore, the electric field intensity is also presented for understanding light coupling, propagation, and absorption nature of GaAs grating under variable incidence angles and magnetic field strengths. The relative study is useful to the thermal radiative design in optical instruments.

We report an exciting discovery that the performance loss in MAPbI₃ solar cells due to low purity of PbI₂ can be fully recovered by adding a small amount of Cl source (MACl). The averaged efficiency of MAPbI₃ solar cells using low-purity PbI₂ is 14.16%, whereas that using high-purity PbI₂ is 16.39%. Excitingly, the averaged efficiency of MAPbI₃ solar cells using low-purity PbI₂ is boosted to 16.58% by adding a small amount of MACl into MAPbI₃ precursor, which is comparable to that from high-purity PbI₂. Results from scanning electron microscopy and x-ray diffraction indicate that the morphologies and structures of MAPbI₃ thin films are not affected by the purity of PbI₂ and the addition of small amount of Cl source. Further investigations using open-circuit voltage decay and admittance spectroscopy (AS) reveal that low purity of PbI₂ leads to lower electron lifetime due to higher defect density, whereas the addition of Cl can suppress the defect density, resulting into higher electron lifetime. This discovery may offer a great opportunity for fabricating low-cost, high-efficiency perovskite solar cells using low-purity feedstocks, which would definitely expedite the development of environment-friendly perovskite solar cells.

Strong luminescent coupling (LC) effect in a multijunction solar cell (MJSC) allows better current balance among its subcells. The temperature dependence of wafer-bonded III-V on silicon (Si) MJSCs with LC effect was investigated. Experimentally, this was explored through light current density–voltage (J  –  V) characteristic measurements, external quantum efficiency measurements, and laser beam-induced current mapping of InGaP/AlGaAs//Si triple junction solar cells at different cell temperatures. Measurement results were analyzed using a quasi-two-dimensional electro-optical prediction model for LC current production and bandgap temperature dependence models of various semiconductors. It was revealed that at lower temperatures, LC current production in the limiting Si bottom cell resulted in a larger absolute LC quantum efficiency difference. At 15°C, the absolute LC quantum efficiency difference calculated was 0.17%, which indicates potential current production improvement if vertical LC current is made uniform.

Strong luminescent coupling (LC) effect reduces current mismatch in III-V-based multijunction solar cells and consequently improves their power conversion efficiency. The LC current production in the Si bottom cell of InGaP/AlGaAs//Si triple junction solar cells having different sizes was investigated to determine the cell area dependence of LC effect. This was probed through laser beam-induced current (LBIC) mapping. The areal mapping was then assessed by obtaining the absolute difference between the quantum efficiencies calculated from the fitted LBIC map and simulated LC current considering uniform distribution using a quasi-two-dimensional electro-optical prediction model. At 9.17 suns concentration difference between the AlGaAs middle cell and the current-limiting Si bottom cell, the absolute LC quantum efficiency differences ranged between 0.16% and 1.68% in various cell sizes, which indicate potential current production increase if the LC current is made uniform.

A four-rod solar pumping concept is proposed for the significant improvement in TEM₀₀-mode solar laser performance. A quadrangular pyramidal reflector is used to separate the focused solar rays from a 2.0-m diameter parabolic mirror into four focal spots. Four laser heads, each one consisting of a double-stage biconical lens/conical pump cavity and a small diameter Nd:YAG rod, are placed at each of the four focal zones. TEM₀₀-mode laser output of 7.22 W is numerically obtained from each rod, resulting in 28.9 W (4  ×  7.22  W) total TEM₀₀-mode power from the four-rod scheme with 9.41  W  /  m² collection efficiency. This value is 2.5 times more than that of the numerically calculated laser power collection efficiency from a single-rod pumped by the same parabolic mirror. A brightness conversion efficiency of 0.86% is achieved. Substantial improvements in TEM₀₀-mode solar laser stability and thermal performance are also numerically demonstrated.

The understanding of actual flux distribution, on the receiver surface of a compound parabolic concentrator (CPC), is a foundational requirement as well as a prime constraint for various applications such as low concentrated solar thermal, photovoltaic, hybrid systems, and other optical systems. As an outcome of recent advancements in the low concentrating medium temperature solar system, CPC concentrator research is attracting a lot of attention. However, poor understanding of flux distribution on the receiver of CPC and effect of manufacturing process on performance require to be enhanced to facilitate extensive applications. The present research reports the precise pattern of distribution of flux on the receiver surface of four sun concentration CPC, ranging from the minimum flux value of 856  W  /  m² to maximum of 27896  W  /  m² for light incidence input of 1000  W  /  m² on aperture of CPC. The present work reports distinct experimental and simulation flux distribution pattern output, which can enable perfect design of a light receiver to achieve efficient light harvesting. In our research work, the four-sun concentrating truncated CPC with plane receiver geometry is manufactured by discriminated laser cutting method. The flux distribution of CPC is investigated through ray tracing simulation and experimentally evaluated. The understanding of distinct flux distribution pattern with mathematical model combined with scalable fabrication technique guides it toward efficient solar energy harvesting.