Guest editors provide an introduction to the special section on Advanced Materials and Devices for Solar Driven Liquid Fuel and Hydrogen Production.

Nanosized semiconductors with hierarchical structures are attractive for use as catalysts. Development of high porous structures, to this end, has received intense interest. By using a well-defined titanium-based metal–organic framework, i.e., MIL-125(Ti), as a template, we report the synthesis of Ni-doped mesoporous TiO₂ nanocrystals with tablet morphologies. While the obtained Ni-TiO₂ composites could be used for photoreduction of CO₂ in the presence of water vapor, this photocatalytic property could be largely improved by further deposition of Ag nanoparticles. In principle, Ni species in the lattice matrix lead to the formation of impurity levels in the bandgap of TiO₂, promoting both light absorption and charge separation. On the other hand, Ag, as a cocatalyst, can trap electrons and simultaneously activate the C═O bonds from the adsorbed CO₂. Our results demonstrate that 1.0% Ag/0.5% Ni-TiO₂ photocatalyst exhibits the highest activity. The yields of CO and CH₄ reach 14.31 and 279.07  μmol  /  g, respectively, for a 3-h reaction. We believe the strategy based upon the synergy of Ni doping and Ag loading can be extended to other photocatalytic systems.

Sacrificial reagents (SRs) are widely used in photocatalytic H₂-evolution systems, and the physical/chemical properties of SRs may be changed after mixing. In our study, triethanolamine, methanol, and lactic acid were selected as three kinds of typical organic SRs, which were of alkaline amine, neutral alcohol, and acidic carboxylic acids, respectively. Graphic carbon nitride (g-C₃N₄) and titanium dioxide (TiO₂), which are of metal-free polymerized-organic and metal-oxide inorganic semiconductors, respectively, were selected as two kinds of typical photocatalysts. By measuring and comparing the photocatalytic H₂-evolution performance of g-C₃N₄ and TiO₂ in single-sacrificial-reagent systems, corresponding binary-sacrificial-reagent systems, and trinary-sacrificial-reagent (TSR) systems, the effects of mixed-sacrificial-reagents (MSRs) on H₂ evolution over these two typical photocatalysts were investigated. It was found that the photocatalytic H₂-evolution rates could be enhanced by mixing appropriate SRs to corresponding photocatalysts, for instance, TiO₂ showed the best photocatalytic performance in 20% TSR system. However, g-C₃N₄ showed the best photocatalytic performance in 20% triethanolamine compared with MSR systems. The effects of MSRs on H₂ evolution over typical photocatalysts could be explained by the adsorptivity between SRs and photocatalysts. Functional groups of SRs that are concerned with the adsorption between SRs and photocatalysts might change in the MSR systems. The weakening of adsorption between SRs and photocatalysts led to the decreased photocatalytic H₂ evolution rates over photocatalysts. We provide useful guidance to the design of MSR systems in order to promote the photocatalytic H₂ evolution.

The ultimate solar radiation received by solar systems is the result of being absorbed and scattered by aerosols, and it is mainly influenced by the geometric structure and composition of the aerosol particles, which can be determined by the formation process. Samples of atmospheric aerosol particles were collected in Harbin from February to April 2019. Gravimetric analysis, transmission electron microscopy, and liquid phase ion chromatography were used to analyze the morphology, mixed structure, and water-soluble ion physicochemical properties of particulate samples. The results showed that the average concentration of particulate matter in dust weather was 648.31  μg  /  m³. The main mixed structure was an external mixed structure, accounting for 58%, and the mass concentration of water-soluble ions accounted for ∼3.6  %   of the total suspended particles. In haze weather, the average concentration of particulate matter was 319.90  μg  /  m³ and the main mixed structure was a core–shell structure, accounting for 60%. The mass concentration of water-soluble ions accounted for ∼11.9  %   of the total suspended particles.

A series of ZnO/CdS photoelectrodes with three-dimensional (3-D) structure were synthesized by two-step hydrothermal method. The photoelectrodes were characterized by x-ray diffraction, UV–vis absorption spectrum, and field emission scanning electron microscope. The results confirmed that all samples have similar hierarchical structure composed of CdS sheets and ZnO nanorod. In particular, the sample fabricated by the CdCl₂ precursor as the Cd source gave the wider band gap and more porous structure. The photoelectrochemical performance of the samples was estimated by photocurrent density testing in the solution under irradiation. The sample prepared by the CdCl₂ precursor exhibited higher photocurrent density than the other three samples due to its 3-D structure, wider band gap, and more porous morphology.

A hydrothermal method was used to synthesize zinc oxide (ZnO) with different exposure faces. Only when the ratio of OH⁻  /  Zn^2  + is 2/1, ZnO with different morphologies and exposure faces can be obtained by controlling the amount of the polyvinylpyrrolidone as a capping agent. Five samples with representative morphology and wurtzite crystal structure were selected from 28 different synthesis conditions. Their optical, surface charged, and photocatalytical properties are closely related to the exposed faces. The ultraviolet fluorescence emission is related to the nonpolar faces in the low index exposure face. All samples are n-type semiconductors and oxygen element is lacking compared to Zn. There is a great possibility that the oxygen vacancy is the oxygen defect that causes the visible fluorescence emission of the nanosheet. Samples are all positive-charged on the surface. The surface charge is not only related to the particle size but also directly affected by the polarity of exposed face and the missing atoms of the sample. The photocatalytic activity of ZnO with nanocolumn morphology is the best, due to high exposure ratio of the polar faces, maximum positive charge, and moderate particle size.

Zeolitic imidazolate framework (ZIF-67) precursor was successfully synthesized, which was supported by one-dimensional (1-D) cobalt alginate fibers. After the pyrolysis at 900°C under N₂ atmosphere, the composites were converted to 1-D carbon-fiber-coated Co@N-doped porous carbon (CoNC-CF-900), acting as efficient oxygen reduction reaction (ORR) electrocatalysts. We investigated the effect of different pyrolysis temperatures on electrocatalytic activities of the obtained samples. The CoNC-CF-900 demonstrated excellent ORR performance, possessing the half-wave potential (E_1/2) of 0.833 V, the onset potential of 0.926 V, the limiting current density of −5.56  mA cm^−  2, and excellent stability under four-electron transfer pathway.

Increasing oil spill accidents and oil industrial wastewater have led to the frequent occurrence of oily contaminants. To remedy these environmental risks, separating oil/water mixtures by absorbent materials has shown great potential. However, viscous oils are difficult to clean up with conventional materials because of their high viscosity with respect to practical applications. A photothermal (PMSQ)-vinyltrimethoxysilane (VTMS)-polypyrrole (PPy) xerogel was fabricated to heat the viscous oil by utilizing the photothermal property of PPy. The chemical structure and micronano morphology of the obtained composite xerogel were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and contact angle goniometry. Experiments of oil adsorption show that the PMSQ-VTMS-PPy xerogel could be applied for viscous oil/water mixture separation, exhibiting excellent properties such as water-repellency, high oil/water separation capacity, adequate buoyancy, good reusability, and easy fabrication. Such a remarkable performance of the PMSQ-VTMS-PPy photothermal xerogel is caused by the fact that crude oil could be heated by harvesting sunlight to reduce the viscosity of oil and achieve the goal of rapidly separating the oil/water mixture. Because of the facile and scalable merits, the one-pot sol–gel method presented is very suitable for industrial uses.

To develop a photo-Fenton catalyst that works under mild conditions, we report the fabrication of Fe₂O₃  /  g-C₃N₄ composite via a simple two-step calcination process for the degradation of phenol under room temperature, neutral solution, and simulated sunlight. The photo-Fenton catalytic degradation constant of the Fe₂O₃  /  g-C₃N₄ composite is 7.07 and 7.62 times that of Fe₂O₃ and g-C₃N₄, respectively. The limited size of Fe₂O₃ and partial reduction of Fe^3  + in the Fe₂O₃  /  g-C₃N₄ composite promotes the production of   ·  OH radical. The Z-mechanism with efficient charge separation efficiency contributes to the enhanced photo-Fenton catalytic performance.

Efficient electron transport layers (ETLs) play a pivotal role in the performance of solar cells. In recent years, Indium sulfide (In₂S₃) has been studied as a promising ETL in CuInGaS(e)₂, Cu₂ZnSnS(e)₄, and perovskite solar cells. Despite several studies on spray-deposited In₂S₃, there is no complete experimental investigation on In₂S₃ thin films. The effect of the molar ratio of S/In and the type of indium precursor on the structural, morphological, optical, and electrical properties of sprayed-In₂S₃ layers has been studied. Films were characterized using x-ray diffraction, scanning electron microscopy (SEM), optical transmission (UV-Vis), Mott–Schottky analysis, four-point probe, and cyclic voltammetry measurements. The crystallinity and morphological characteristics are strongly influenced by the type of indium salt, where indium acetate precursor results in a highly porous film compared with nitrate and chloride precursors. The chloride precursor demonstrates better crystallinity and considerably lower sheet resistance. All films are n-type with a carrier concentration in the range of ∼2  ×  10¹⁷ to ∼2  ×  10¹⁸  cm^−  3, with an indirect bandgap of 2.0 eV.

Numerical simulations based on solving the Maxwell equations provide a robust and efficient approach to obtaining optical properties of plasmonic metal nanoparticles (NPs), but they have high computational costs when considering the real conditions of incorporated NPs such as random distribution and nonuniform size. Therefore, an effective medium theory, taking into account light scattering on the surface of NPs and light concentration by localized surface plasmon resonance, has been employed to obtain optical properties of randomly embedded spherical NPs with nonuniform radii into GaAs. The results are input into an optoelectrical model of graphene/GaAs Schottky barrier solar cells (SCs), calibrated by the experimental data, to compare the performance of plasmonic graphene/GaAs SCs with the incorporation of different metal NPs of Au, Ag, Al, and Cu. Furthermore, the effects of the number of graphene layers, the radius of NPs, and the amount of size dispersion on the photovoltaic parameters of plasmonic graphene/GaAs SCs have been investigated. It is demonstrated that increasing the radius and size dispersion of NPs, by inducing an inhomogeneous broadening and an increase of plasmon band amplitude, enhances the efficiency of plasmonic graphene/GaAs SCs.

Perovskite-based solar cells (PSCs) have opened the possibility of cost-effective, high-efficiency photovoltaic conversion. However, their instabilities prevent them from commercialization. One of the instability triggers has been attributed to the mobile ions flowing into the carrier transport layer(s). To study the effect of this ionic migration, a numerical PSC model is developed, considering electronic and ionic mixed drift-diffusion transport both in the perovskite and the hole transport layer. The inverted PSC architecture, phenyl-C61-butyric acid methyl ester (PCBM)/perovskite/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with two heterojunctions, is analyzed. The effect of the ionic migration on the performance of the PSCs has been analyzed by (1) the variation of the ionic mobile concentration and (2) the modification of the local trapping density. The current–voltage (J–V) and capacitance–voltage characteristics show that the electric field in the bulk can be screened by the ionic distribution modifying the effective built-in voltage. At high ionic concentrations, the electric field at the interfaces is also affected, hindering the charge extraction. The simulations show that the short circuit current is therefore strongly modified.

We present measured optical absorptivity, emissivity, and maximum solar-heated temperatures for micropatterned molybdenum. The molybdenum samples were fabricated using laser micromachining and characterized using an integrating sphere and an infrared microscope. In-air solar simulator-heated temperature results for the molybdenum samples with different microstructures are presented, and COMSOL modeling is then used to predict in-vacuum maximum temperatures. A vacuum chamber was developed to reduce the convection heat loss with a mount designed to minimize conduction loss, and a maximum measured temperature of 413°C was obtained.

Traditional Cu  (  InGa  )  Se₂ (CIGS) solar cells consist of an Mo bottom contact, p-type CIGS absorber layer, n-type CdS buffer layer, and ZnO window layer including a very thin intrinsic ZnO layer topped with an Al-doped ZnO transparent conducting oxide layer that was simulated by an Silvaco technology computer aided design simulator. The thickness of the layers and other parameters were limited to the values reported in the literature. The simulator was examined to affirm its functionality, and a step-by-step method was applied to optimize the baseline structure. The first modification was the substitution of the conventional CdS buffer layer with a nontoxic n-type ZnO buffer layer. The substituted ZnO buffer layer showed an effective band alignment and led to a remarkable improvement in cell performance. The second modification was the inclusion of different antireflective coatings, such as Al₂O₃, MgO, SnO₂, and CdO, to enhance light trapping. Among them, CdO caused the highest efficiency. The optimization process was followed by replacing a very-thin (750 nm) CIGS layer containing three sublayers with dual-graded Ga contents. A trapezoidal gradient profile was tested and showed a significantly increased internal electric field, which assisted in raising the efficiency of the device. The last simulation concluded that the efficiency of a CIGS solar cell was 19.21% and the efficiency related to the baseline structure was enhanced by 36.24%.

We reduce the problem of asymmetrical distribution of carriers (electrons and holes) by engineering the last barrier and electron blocking layer (EBL) of green indium gallium nitride (InGaN)-based multiquantum well light-emitting diodes. We employ stair-engineered EBL with a graded InGaN last quantum barrier to enhance the device performance. The efficiency droop ratio of the proposed device is ∼15  %   at 100  A  /  cm². Similarly, the light output power is also enhanced by about three times, as compared to the reference structure. In addition, a carrier transport issue across the active region is also mitigated in our design.

Luminescent solar concentrators (LSCs) have been studied for decades as an alternative to conventional lens-based optical concentrators for improving the performance and lowering the cost of high-efficiency photovoltaic solar converters. However, the Stokes shift from luminophores that comprise the LSC entails that the strategy cannot achieve the well-known Shockley–Queisser conversion efficiency limit of 33.7%, even theoretically. We show how aligned semiconductor nanorods with anisotropic dipolar photoluminescence can partially overcome losses due to the Stokes shift. We also outline LSC designs with conversion efficiency >33.7  %   and highlight how nanorods relax the demands on solar trackers in these proposals. Our analysis predicts efficiency increases even when nonradiative loss is comparable to current GaAs cells and when our models incorporate the experimentally measured anisotropy of colloidal dot-in-rod CdSe/CdS nanoparticles that we synthesized for this study. Fundamentally, these improvements result from the angular redistribution of light energy provided by the anisotropic, Stokes-shifted nanorod luminescence.

Cadmium selenide (n-CdSe) thin films were grown on a silicon substrate with a polished surface and applied to the Schottky type device structure. The n-CdSe thin films produced depended on various deposition times at 70°C by the use of the chemical bath deposition technique. XRD results show that the fabricated thin films consist of both cubic and hexagonal crystal systems. The morphology of CdSe was formed in nanograins and nanowire structures with respect to deposition times of 6 and 10 h, respectively. In addition to structural analysis of CdSe thin films, CdSe nanowires were used as an interfacial layer in a metal–semiconductor device to investigate its effects on the electrical and photosensitive characteristics of the device. As well as under forward bias current–voltage (I  −  V) conditions, the space charge limited current conduction behaviors were identified at low voltages. The results showed that the film produced at 10 h has a better performance compared to that produced at 6 h in terms of increased electric current.

An indium arsenide photovoltaic cell with gold front contacts is designed for use in a near-field thermophotovoltaic (NF-TPV) device consisting of millimeter-size surfaces separated by a nanosize vacuum gap. The device operates with a doped silicon radiator maintained at a temperature of 800 K. The architecture of the photovoltaic cell, including the emitter and base thicknesses, the doping level of the base, and the front contact grid parameters, is optimized to maximize NF-TPV power output. This is accomplished by solving radiation and charge transport in the cell via fluctuational electrodynamics and the minority charge carrier continuity equations, in addition to accounting for the shading losses due to the front contacts and additional series resistance losses introduced by the front contacts and the substrate. The results reveal that these additional loss mechanisms negatively affect NF-TPV performance in a non-negligible manner and that the maximum power output is a trade-off between shading losses and series resistance losses introduced by the front contacts. For instance, when the cell is optimized for a 1  ×  1  mm² device operating at a vacuum gap of 100 nm, the losses introduced by the front contacts reduce the maximum power output by a factor of ∼2.5 compared with the idealized case when no front contact grid is present. If the optimized grid for the 1  ×  1  mm² device is scaled up for a 5  ×  5  mm² device, the maximum power output is only increased by a factor of ∼1.08 with respect to the 1  ×  1  mm² case despite an increase of the surface area by a factor of 25. This work demonstrates that the photovoltaic cell in a NF-TPV device must be designed not only for a specific radiator temperature but also for a specific gap thickness and device surface area.

We investigate the role of luminescence effects on the analysis of solar cell properties. InGaP/GaAs tandem solar cells fabricated using hydride vapor phase epitaxy have a luminescent coupling (LC) efficiency of 0.6% from the top to the bottom subcell. We investigate the impact of LC on subcell current–voltage curve analysis using electroluminescence (EL) measurements. EL efficiency measurements were performed using a reference InGaP single-junction device. It was found that the luminescence extraction from the top subcell, and therefore its luminescence collection efficiency, is lower than that from the bottom subcell. This is due to LC from the top subcell to the bottom subcell. By considering the luminescence extractions of each subcell, more reasonable subcell voltages than those found by conventional methods can be obtained.