Optical component designs for concentrating photovoltaic systems with three different multijunction solar cells (MJSCs) are optimized to yield maximum system efficiencies under standard test conditions, specifically uniform illumination. Optimization uses an integrated optoelectrical approach with ray tracing of the optical train to generate an irradiance profile for input to the cell’s distributed circuit model. These cells, a three-junction lattice-matched (3JLM) solar cell, a three-junction lattice-mismatched inverted metamorphic (3JIMM) solar cell, and a four-junction lattice-matched (4JLM) solar cell, were individually designed for maximum efficiency at 1000×. The optical train introduces losses, modifies the spectrum, and produces a spatially nonuniform profile across the cell. We decouple spectral modification from spatial nonuniformity to separately determine their individual impacts on system efficiencies, finding the optimal set of optical design parameters for each case. Spectral modification yields modest loss penalties (from 1.0% to 1.6%, relative to the MJSC), but the impact of nonuniformity is more significant and cell dependent, with relative loss penalties of 1.1%, 3.8%, and 2.3%, for 3JLM, 3JIMM, and 4JLM, respectively. While spectral modification does not significantly impact design parameters, spatial nonuniformity does, with absolute losses of 1% and 3.4% if 3JIMM and 4JLM cells are used in a 3JLM optimized system, respectively.

A two-dimensional finite-element model was developed to simulate the optoelectronic performance of a Schottky-barrier solar cell. The heart of this solar cell is a junction between a metal and a layer of n -doped indium gallium nitride ( In ξ Ga 1 − ξ N ) alloy sandwiched between a reflection-reducing front window and a periodically corrugated metallic back reflector. The bandgap of the In ξ Ga 1 − ξ N layer was varied periodically in the thickness direction by varying the parameter ξ ∈ ( 0,1 ) . First, the frequency-domain Maxwell postulates were solved to determine the spatial profile of photon absorption and, thus, the generation of electron–hole pairs. The AM1.5G solar spectrum was taken to represent the incident solar flux. Next, the drift-diffusion equations were solved for the steady-state electron and hole densities. Numerical results indicate that a corrugated back reflector of a period of 600 nm is optimal for photon absorption when the In ξ Ga 1 − ξ N layer is homogeneous. The efficiency of a solar cell with a periodically nonhomogeneous In ξ Ga 1 − ξ N

In recent years, the development of smart textiles has attracted great attention. Such textiles can contain small electrical devices, which need a power supply. Dye-sensitized solar cells, which can be produced from nontoxic, cheap, low-purity materials, could fill this purpose. However, to reach reasonable cell properties, sintering the TiO2 layer on the substrate is necessary. Unfortunately, only a few textile materials can withstand a sintering process at high temperatures. Therefore, it is important to find an optimal temperature leading to a reasonable improvement of the cell characteristics without damaging the textile substrate. The influence of the sintering temperature on different properties is investigated. For this, the surface properties of the TiO2 coating, such as adhesion to the substrate, dye adsorption characteristic, and film stability, are investigated on different substrates, i.e., a glass plate, a stainless steel nonwoven fabric, and a carbon woven fabric. Two commercially available TiO2 sources are used: a TiO2 dispersion obtained from Man Solar and a water-based solution of TiO2 particles purchased from Kronos. The influence of the sintering temperature on short-circuit current and open-circuit voltage of solar cells on the aforementioned substrates is also examined.

A flat titanium sheet with microholes (FTS-MH) has been utilized to fabricate transparent conductive oxide-less dye-sensitized solar cells (TCO-less DSSCs) in back contact device architecture. Utilization of FTS-MH to fabricate a TCO-less photoanode offers several advantages in terms of simplicity and ease of fabrication as compared with the TCO-less DSSCs structure reported previously. Hydrogen peroxide (H2O2) surface treatments on FTS-MH have shown important factors to enhance the photoanode properties. H2O2 surface treatment is able to change the surface morphology of FTS-MH, and the created anatase titanium dioxide (TiO2) nanostructures increase the surface contact between the FTS-MH and the coated mesoporous TiO2. Electrochemical impedance investigations reveled that improvements of the FTS-MH/TiO2 and TiO2/dye/electrolyte interface led to hampered charge recombination resulting in enhancement of both short-circuit current density and open-circuit voltage, respectively. Even after removal of both TCO layers, our complete TCO-less DSSCs exhibited a power conversion efficiency of 7.25% under simulated solar irradiation.

Using an ideal model for quantum well solar cells, a theoretical work is done to explore the dependence of terminal characteristics of Al0.56Ga0.44As solar cell to quantum well properties. Two systems of constant and variable width multiquantum wells (VWMQW) are considered in the study. Open-circuit voltages, short-circuit current densities, and conversion efficiencies are calculated assuming AM1.5 solar illumination at a cell temperature of 300 K. The assumed VWMQW structures are compared with multiple quantum wells with constant well width.

Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers, and nanofluidic biochemical sensors. We report on the growth of hierarchical GaN nanowires (NWs) by dynamically adjusting the growth parameters using the pulsed flow metal-organic chemical vapor deposition technique. We carried out two step growth processes to grow hierarchical GaN NWs. In the first step, the GaN NWs were grown at 950°C, and in the second, we suitably decreased the growth temperature to 630°C and 710°C to grow the hierarchical structures. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and cathodoluminescence measurements. These kinds of hierarchical GaN NWs are promising for allowing flat band quantum structures that are shown to improve the efficiency of LEDs.

Today, freeform micro-optical structures are desired components in many photonic and optical applications, such as lighting and detection systems, due to their compactness, ease of system integration, and superior optical performance. The high complexity of a freeform structure’s arbitrary surface profile and the need for high throughput upon fabrication require sophisticated approaches for their integration into a manufacturing process. In this paper, we discuss a smart fabrication process of freeform micro-optical elements that ranges from their design by optical simulations to their cost-efficient fabrication by maskless laser direct write lithography (MALA) and replication from the as-fabricated master by imprinting. Aided by profilometry and optical microscopy, the fidelity of the fabricated freeform micro-optical elements to the design is characterized. Finally, the light intensity distribution on a target plane affected by the freeform micro-optical element illuminated with a light-emitting diode is determined and compared with the predicted one.

There is a great interest in the development of high-power, high-efficiency, and low-cost quasicontinuous wave (QCW) diode laser bars and arrays for pumping solid state lasers. We report on the development of kW-class 88x-nm diode laser bars that are based on a bipolar cascade design, in which multiple lasers are epitaxially grown in electrical series on a single substrate and separated by low-resistance tunnel junctions with resistance as low as 8.0×10−6  Ω-cm2. QCW power of 630 W was demonstrated in a 3-mm-wide minibar with 3-mm cavity length. Peak efficiency of 61% was measured with 200  μs and 14 Hz pulses, at 10°C. Further power scaling was demonstrated in a 1-cm-wide bar with 3-mm cavity length, where a record peak power of 1.8 kW was measured at 1-kA drive current. Ongoing work for further power scaling includes development of triple-junction diode laser bars.

W ions were doped into ZnO nanorod arrays hydrothermally grown on the F-doped tin-oxide-coated glass substrates via an advanced ion implantation technique for photoelectrochemical (PEC) water splitting under visible light. It was found that W incorporation could narrow the bandgap of ZnO and shift the optical absorption into visible light regions obviously, with the one-dimensional nanorod structure maintained for superior charge transfer. As a result, the W-doped ZnO nanorod arrays exhibit considerable PEC performance relative to ZnO nanorod arrays under visible light illumination (λ>420  nm), with photocurrent density achieved up to 15.2  μA/cm2 at 1.0 V (versus Ag/AgCl). The obtained PEC properties indicate that ion implantation can be an alternative approach to develop unique materials for efficient solar energy conversion.

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Cd0.5Zn0.5S photocatalyst was prepared by a hydrothermal method and characterized by x-ray diffraction and UV–Vis absorption spectroscope techniques. Using the pollutant formaldehyde as an electron donor, the photocatalytic H2 evolution from water splitting under visible light (λ≥420  nm) irradiation was examined. It was found that formaldehyde can notably enhance photocatalytic H2 evolution with its simultaneous degradation. An alkaline condition also was beneficial to the photocatalytic H2 evolution. The effect of formaldehyde concentration on the H2 evolution rate was consistent with a Langmuir–Hinshelwood kinetic model. The stability test indicated that the catalyst was rather stable during 20-h irradiation and the average apparent quantum yield amounted to 3.1% under visible light irradiation (λ≥420  nm) and 25.7% at 420 nm even without any cocatalysts. The possible mechanism was discussed.

Spectrum-splitting is a multijunction photovoltaic technology that can effectively improve the conversion efficiency and reduce the cost of photovoltaic systems. Microscale PV design integrates a group of microconcentrating photovoltaic (CPV) systems into an array. It retains the benefits of CPV and obtains other benefits such as a compact form, improved heat rejection capacity, and more versatile PV cell interconnect configurations. We describe the design and performance of a two-junction holographic spectrum-splitting micro-CPV system that uses GaAs wide bandgap and silicon narrow bandgap PV cells. The performance of the system is simulated with a nonsequential raytracing model and compared to the performance of the highest efficiency PV cell used in the micro-CPV array. The results show that the proposed system reaches the conversion efficiency of 31.98% with a quantum concentration ratio of 14.41× on the GaAs cell and 0.75× on the silicon cell when illuminated with the direct AM1.5 spectrum. This system obtains an improvement over the best bandgap PV cell of 20.05%, and has an acceptance angle of ±6  deg allowing for tolerant tracking.

Ultrathin amorphous silicon hydrogenated (aSi-H) solar cells grown on a one-dimensional (1-D) dielectric subwavelength gratings improve the short circuit current by a factor of more than 51% when compared with conventional, flat ultrathin aSi-H devices. This improvement is possible due to several mechanisms. In addition the increase in exposed area caused by the nanostructured surface, a reliable computational electromagnetic evaluation of the interaction of the solar spectrum with the cell structure demonstrates that absorption at the active layer is enhanced and also reflectivity is decreased. In addition, the absorbed power at the nonactive layers is larger, helping to increase the temperature and mitigate the Staebler–Wronski effect. The detailed analysis of the power flux inside the structure has also shown that funneling and guiding mechanism are at play, increasing the optical path within the active layer that produces a better performance of the cell.

Light concentration has proven beneficial for solar cells, most notably for highly efficient but expensive absorber materials using high concentrations and large scale optics. Here, we investigate the light concentration for cost-efficient thin-film solar cells that show nano- or microtextured absorbers. Our absorber material of choice is Cu(In,Ga)Se2 (CIGSe), which has a proven stabilized record efficiency of 22.6% and which—despite being a polycrystalline thin-film material—is very tolerant to environmental influences. Taking a nanoscale approach, we concentrate light in the CIGSe absorber layer by integrating photonic nanostructures made from dielectric materials. The dielectric nanostructures give rise to resonant modes and field localization in their vicinity. Thus, when inserted inside or adjacent to the absorber layer, absorption and efficiency enhancement are observed. In contrast to this internal absorption enhancement, external enhancement is exploited in the microscaled approach: mm-sized lenses can be used to concentrate light onto CIGSe solar cells with lateral dimensions reduced down to the micrometer range. These micro solar cells come with the benefit of improved heat dissipation compared with the large scale concentrators and promise compact high-efficiency devices. Both approaches of light concentration allow for reduction in material consumption by restricting the absorber dimension either vertically (ultrathin absorbers for dielectric nanostructures) or horizontally (microabsorbers for concentrating lenses) and have significant potential for efficiency enhancement.