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Fabrication of Thin III-V Solar Cells on Ni Films using Electroless Ni Deposition
Thin solar cells are inherently fragile, and must be properly supported during fabrication, handling and use. Metal films can provide this support, but accomplishing this can be challenging. Here we describe a method for fabricating thin III-V solar cells on Ni films, using electroless deposition to deposit a thick (10-50 um) Ni film onto the bottom of an inverted III-V solar cell prior to substrate removal. Cells have been fabricated on both rigid and flexible supports with no loss of performance when compared to cells processed using standard inverted-cell processing.
Stability of Tin-Lead Halide Perovskite Solar Cells
Tin-lead perovskites have low band gaps (1.2 eV - 1.4 eV) that offer complementary absorption spectra to mixed halide perovskites with band gaps in the range of 1.6 eV - 1.85 eV. In combination, tin-lead and mixed halide perovskites can be used to make efficient all-perovskite tandem solar cells. While these can achieve high efficiency, they are hampered by the unproven longterm stability of tin-containing perovskites. We make the first demonstration of tin-lead perovskite solar cells that pass benchmark 1000-hour tests of stability under stressors of heat, light, and atmospheric exposure. We identify that mixed tin-lead perovskites oxidise by a different chemical pathway, one that is much less favourable, than the oxidation pathway followed by pure tin perovskites, making them significantly more stable. Fortuitously, mixed tin-lead perovskites also have band gaps that are close to ideal for the rear cell of an all-perovskite monolithic two-junction tandem. Beyond selecting the composition of the perovskite to be one that has inherently suppressed tendency to oxidise, we also fabricate a novel heterojunction-based architecture that eliminates the commonly used acidic PEDOT:PSS layer, which leads to enhanced stability. By packaging the resulting solar cell in a glass-on-glass package with a pliable low-elastic-modulus polyolefin encapsulant and a butyl rubber edge seal, we also demonstrate that the low band gap perovskite solar cell that passes the IEC damp heat test for thin film solar cells - a milestone that demonstrates the removal of a significant impediment to the commercialization of high efficiency perovskite tandem solar cells.
Additive Manufacturing of Corrosion Resistant UHTC Materials for Chloride Salt-to-sCO2 Brayton Cycle Heat Exchangers
The objectives of the project include: (1) screen high-purity, high density ultra-high-temperature ceramics (UHTCs) for chloride salt corrosion resistance, (2) develop binder-jet additive manufacturing and sintering for ZrB 2 -MoSi 2 blends using literature and experiments to demonstrate feasibility, and (3) evaluate chloride salt corrosion resistance of additively manufactured ZrB 2 -MoSi 2 . These initial objectives support the development of a durable and reliable ultra-compact high-efficiency salt-to-sCO 2 heat exchanger for closed-loop Brayton power cycles based on corrosion resistant, high-strength, thermally conductive UHTC materials and novel designs enabled by additive manufacturing. The UHTC materials are also abrasion resistant so that they could be applicable to all three thermal carrier media pathways identified in the CSP Gen3 Roadmap.
Distinguishing Bulk and Surface Recombination By Measuring and Modeling Ultrafast Carrier Dynamics
Distinguishing Bulk and Surface Recombination By Measuring and Modeling Ultrafast Carrier Dynamics The combination of modeling with TRTS and TRPL under multiple excitation conditions improves accuracy and precision of parameter estimation. Ultrafast carrier dynamics can link materials, processing, and device performance to direct the design of more efficient solar cells.
Exploring the impact of the local environment on charge transfer states at molecular donor-acceptor heterojunctions
This program explored a broad range of charge transfer (CT) states in organic solar cells with the goal of understanding how molecular energetics, structure, and morphology influence CT state energy and dynamics, and how this in turn influences solar cell performance. We identified new types of delocalized CT states at ordered molecular heterojunctions, determined the factors that dictate CT state energetic disorder in bulk heterojunctions, determined that hot CT state dissociation is negligible for most systems, that the occupation of CT states is generally non-thermal in disordered heterojunctions, and that quasi-equilibrium generally does not hold in organic solar cells. These findings allowed us to demonstrate the lowest loss in potential of any organic solar cell to date and provide valuable guidance for designing higher efficiency organic solar cells in the future.
Scalable, Infiltration-Free Ceramic Matrix Composite Manufacturing for Molten Salt Receiver (SIF-CMC)
Ceramic Matrix Composite (CMC) with high thermomechanical properties is a promising material class for Concentrated Solar Power but current use is limited by a long and tedious manufacturing process with high costs and poor scalability. SIF-CMC provides a novel way to simplify the manufacturing process by dramatically increasing the char yield of the matrix from polymer to ceramic, which makes the CMC affordable and scalable.
Photovoltaic Cable Jackets: A Comparison of Representative Products Using Combined-Accelerated Stress Testing [Slides]
Photovoltaic (PV) cables facilitate the distribution of electricity collected from modules to the energy grid. Durable cabling enables continuous operation of PV installations, whereas cables with a lifetime less than the modules must be replaced - reducing electricity generation and adding to the operating expense. This study primarily focusses on the aging of the key cable types using the combined-accelerated stress testing (C-AST) protocol. Representative cables for utility, building, and control/auxiliary applications were examined. Cable jacket materials examined include: polyolefin, polyethylene, polyamide, poly(vinyl chloride), chlorinated polyethylene, thermoplastic elastomer, and ethylene propylene diene monomer rubber. Specimen characterizations applied include: optical microscopy, mechanical profilometry, instrumented indentation, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). A variety of performance and durability characteristics were observed, depending on the base material, polymer formulation, and jacket color. The results from C-AST are analyzed and discussed relative to a recent industry survey on electronic balance of system components in addition to a recent study where similar cables were aged using steady state ultraviolet weathering (International Electrotechnical Commission Technical Specification 62788-7-2). Recommendations are made for the screening, industry qualification, and service life prediction of PV cable jackets.
UHTC-TPMS Heat Exchangers for Concentrating Solar Power Applications with Thermal Energy Storage in Molten Chlorides
Concentrating solar power (CSP) plants convert energy from sunlight into electricity. Generally, a heliostat field is used to reflect sunlight and concentrate it onto a receiver, which heats the receiver and/or the media flowing through it. A flow loop transports the media through the system to a heat exchanger before returning the media back to the receiver to be reheated. The heat extracted by the heat exchanger is then converted into electricity using a conventional heat engine.
From Femtoseconds to Gigaseconds: The SolDeg Project to Analyze and Mitigate the Performance Degradation of a-Si:H/c-Si Heterojunction Solar Cells
We pursued two major projects. In the first, we studied the degradation of a-Si/c-Si Heterojunction cells. We substantially expanded our previously developed SolDeg platform, and incorporated hydrogen into it. We also expanded the capabilities of SolDeg by developing a three channel model for a very efficient way to determine long term junction dynamics. The first main result was that we identified hydrogen drifting away from the interface as a key degradation channel. The second was that we developed and proposed the concept of a “reverse silicon density gradient” in the a-Si layer that had the promise of reducing degradation by up to 80%. In the second project, we studied the degradation of TOPCon solar cells. We again identified a key degradation channel, which in these cells was the formation of pinholes across the oxide layer. We then again were able to develop and to propose a way to dramatically reduce degradation by discovering that tuning the hydrogen concentration forms a sharp and deep minimum of the recombination current.
A Scalable Solution Route to Porous Networks of Nanostructured Black Tungsten
This paper studied the feasibility of a new solution-processed method to manufacture black tungsten nanostructures by laser conversion of tungsten hexacarbonyl precursor on the Inconel 625 substrate under argon atmosphere at ambient pressure. The results show that sublimation of the precursor can be prevented if the decomposition temperature (>170 °C) is achieved using the laser heating method. Three different laser powers from 60–400 W were used to investigate the role of laser parameters on the conversion. It was found that lower laser power of 60 W resulted in a mixture of unconverted precursor and converted tungsten. Higher laser powers >200 W resulted in α-W (BCC) in one step without further heat treatment. Different oxygen concentrations from 0.5 ppm to 21 vol% were used in the laser canister to investigate the effect of oxygen concentration on the conversion. It was found that the hard vacuum (>10−4 torr) or hydrogen is not necessary to obtain α-W (BCC). The solar absorptance varied from 63–97%, depending on the amount of precursor deposited on the substrate and oxygen content in the laser canister. This solution-based laser conversion of tungsten precursor is a scalable method to manufacture tungsten coatings for high-temperature applications.
Gallium Oxide Techno-Economic Analysis for the Wide Bandgap Semiconductor Market: Preprint
More than 30% of electrical energy passes through power electronics today with speculation that in the next decade this could grow to 80%. The wide bandgap semiconductor market is already approaching $1 billon USD in 2019 and is projected to be almost $7 billion USD in 2028. Even with its high cost, SiC, is starting to dislodge the incumbent Si technology in some applications, such as hybrid and electric vehicles, due to smaller size, and higher efficiency. We review and report the IHS Markit’s market predictions for wide bandgap semiconductor technologies, and highlight the techno-economic analysis results for the manufacturing cost of Ga2O3 wafers. Specifically, we focus on the potential for Ga2O3 to be more economically advantageous than SiC using current manufacturing methods and then identify opportunities where research can further reduce the volume cost of Ga2O3 wafers.
Evaluating Interconnection Schemes for Semi-Transparent Perovskite Mini-Modules
This work evaluates the critical issues surrounding P1, P2, and P3 scribing for semi-transparent perovskite module integration. We find that P1 scribing procedures are well-translated from other thin-film technologies. P2 scribing is best performed with a mechanical scribe, but remains a source of series resistance. P3 scribing is found to cause an increase in scribing dead area and a potential degradation source.
Solar-Blind Radioluminescence Imaging of Alpha Radiation in Air (Supporting Material).
Abstract not provided.
Robust, Standardized High-Temperature Molten Chloride Salt Reference Electrodes
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Durable Module Materials Consortium (DuraMAT) FY 2021 Annual Report: New Results and a Renewed Consortium
The Durable Module Materials Consortium (DuraMAT) is a multi-lab consortium led by the National Renewable Energy Laboratory, with Sandia National Laboratories, SLAC National Accelerator Laboratory, and Lawrence Berkeley National Laboratory as core research labs. DuraMAT's overarching goal is to discover, develop, de-risk, and enable the rapid commercialization of improved materials, designs, predictive tests, and models for photovoltaic (PV) modules that increase performance, extend lifetime, and enable new applications. Technical results are highlighted throughout this report, and the new projects awarded for FY 2022 address many of the challenges to making 50-year, high-energy-yield modules that were identified in these working groups.
High Temperature Operable, Harsh Environment Tolerant Flow Sensors for Nuclear Reactor Applications
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Laser Welded Edge Seals for Polymer-Free Glass/Glass Modules
This presentation covers fs lasers which enable crack-free and stress-free glass/glass welds. Welds are nearly as strong as the glass (KI, weld ~ KI, glass) and static load test passed, enabling: 1) polymer-free; 2) hermetically sealed; and 3) recyclable modules. Next steps are: 1) follow-on funding; 2) develop feed throughs (metal/glass welds already achieved for other devices); and 3) weld mini modules for further IEC module testing.