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DOE OSTI2020

Machine learning enabled discovery of application dependent design principles for two-dimensional materials

Abstract The unique electronic and mechanical properties of two-dimensional (2D) materials make them promising next-generation candidates for a variety of applications. Large-scale searches for high-performing 2D materials are limited to calculating descriptors with computationally demanding first-principles density functional theory. In this work, we alleviate this issue by extending and generalizing crystal graph convolutional neural networks to systems with planar periodicity and train an ensemble of models to predict thermodynamic, mechanical and electronic properties. We carry out a screening of nearly 45,000 structures for two separate applications: mechanical strength and photovoltaics. By collecting statistics of the screened candidates, we investigate structural and compositional design principles that impact the properties of the structures surveyed. Our approach recovers some well-accepted design rules: hybrid organic-inorganic perovskites with lead and tin tend to be good candidates for solar cell applications and titanium based MXenes usually have high stiffness coefficients. Interestingly, other members of the group 4 elements also contribute to increasing the mechanical strength of MXenes. For all-inorganic perovskites, we discover some compositions that have not been deeply studied in the field of photovoltaics and thus open up paths for further investigation. We open-source the code-base to spur further development in this space.

Venturi, Victor (ORCID:0000000156727549)↗

DOE OSTI2024

Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron

Hybrid magnonic quantum systems have drawn increased attention in recent years for coherent quantum information processing, but too large magnetic damping is a persistent concern when metallic magnets are used. Their intrinsic damping is largely determined by electron-magnon scattering induced by spin-orbit interactions. In the low scattering limit, damping is dominated by intra-band electronic transitions, which has been theoretically shown to be proportional to the electronic density of states at the Fermi level. In this work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic material. We comprehensively study its electronic structure using first-principles density functional theory simulations and account for finite lattice temperature, boron (B) doping, and structure amorphization. Our results indicate that temperature induced atomic disorder and amorphous atomic geometries only have a minor influence. Instead, boron doping noticeably decreases the density of states near the Fermi level with an optimal doping level of 6.25%. In addition, we show that this reduction varies significantly for different atomic geometries and report that the highest reduction correlates with a large magnetization of the material. Furthermore, this may suggest materials growth under external magnetic fields as a route to explore in experiment.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Strong Superexchange in a $d^{9–δ}$ Nickelate Revealed by Resonant Inelastic X-Ray Scattering

The discovery of superconductivity in a $d^{9–δ}$ nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. In this work, we address this question using Ni L-edge and O K-edge spectroscopy of the reduced $d^{9–1/3}$ trilayer nickelates R 4 Ni 3 O 8 (where R = La, Pr) and associated theoretical modeling. A magnon energy scale of ~80 meV resulting from a nearest-neighbor magnetic exchange of J = 69 (4) meV is observed, proving that $d^{9–δ}$ nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O K-edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Scalar flux transport models for self-similar turbulent mixing

A common approach to closing turbulent species flux in multicomponent Reynolds-averaged Navier-Stokes models is to use the standard gradient diffusion approximation. While such an approach has been shown to work well when applied to many canonical turbulent mixing configurations, a gradient diffusion approach is fundamentally limited in its ability to capture complex phenomena such as countergradient transport. For this reason, complicated mixing applications may benefit by treating the turbulent diffusivity with a model transport equation in a manner analogous to second-moment momentum closure in Reynolds-stress transport models. Here, the present work explores the development and application of two different scalar flux transport (SFT) models. Self-similarity constraints are derived for these models, and they are evaluated against gradient-diffusion-based models in several one- and two-dimensional problems of turbulent mixing. It is found that the new SFT models out-perform gradient diffusion models in problems involving rapid acceleration reversal and in problems involving anisotropic transport of materials. In addition, it is found that even a hybrid-SFT approach, in which an SFT equation is utilized along with a gradient diffusion closure, provides some measure of improvement over models that transport the mass flux rather than the scalar flux.

Reynolds-averaged Navier Stokes↗

DOE OSTI2024

A NUMERICAL STUDY OF HEAT TRANSFER IN THE FUEL CELL OF A SOLID OXIDE FUEL CELL-COMBUSTOR

A Solid Oxide Fuel Cell-Combustor (SOFC-C) concept was proposed to address many challenges a traditional fuel cell-gas turbine hybrid system (FC-GT) will have in aerospace applications. By taking advantage of the temperature rise during compression and the combustion of anode off-gas, the SOFC-C eliminates the recuperating heat exchanger usually required for cathode flows, greatly reducing the size and weight (thermal mass) of the system. The fuel cell is one of the key parts of the SOFC-C, so it is desired to understand the heat transfer in the fuel cell. In present work, a computational fluid dynamic (CFD) model was developed to reveal the gas flow and heat transfer in the fuel cell of the SOFC-C. The model includes not only convection heat transfer, but also includes the radiation heat transfer. The modeling results help to optimize the SOFC-C design.

Zhang, Mingkan↗

DOE OSTI2020

Programmable Dynamic Self-Assembly of DNA Nanostructures (Final Technical Report)

This technical report summarizes our research toward the synthesis of active biomolecular materials that take advantage of the biological properties of DNA and RNA, but can operate in non-biological contexts. Our approach takes inspiration from the dynamic assembly and disassembly of cytoskeletal filaments inside cells, and focuses on the generation of artificial filaments with comparable adaptation and responsiveness. We report the construction of DNA nanotube systems that assemble and disassemble reversibly in response to a variety of molecular stimuli including other nucleic acids (DNA and RNA), enzymes, and pH, as well as our progress on developing a reaction network framework to regulate self-assembly. Our DNA polymers are active in that they rely on the programmable energetics of hybridization and on the kinetics of enzymatic reactions to perform assembly and disassembly. Results include experiments and computational models. The research described here was performed between June 15, 2016 and June 15, 2019 at the University of California at Riverside with the support of the collaborative award DE-SC0010595 to PI Elisa Franco at UC Riverside and PI Rebecca Schulman at Johns Hopkins. The report focuses on the research performed by the team of PI Franco. The report also details work performed during a no-cost extension (June 15, 2019 - December 15, 2019) awarded to PI Guillermo Aguilar and PI Franco.

36 MATERIALS SCIENCE↗

DOE OSTI2022

First-principles free energies by hybrid thermodynamic integration for phase equilibria and fission product solubility in molten salts

The overarching goal of this research project is quantitative microscopic modeling of phase diagrams and solubility of actinides and lanthanide-fission products in molten salts for molten salt reactors. Application of molten salts as coolants and liquid fuels for next-generation reactors requires quantitative understanding of phase diagrams, equations of state and transport properties of binary and ternary molten salt mixtures, as well as solubility of fuel, fission products and reactor-wall corrosion products, but these remain beyond the reach of current first-principles computational techniques. We will address this fundamental capability gap using a novel hybrid framework for thermodynamic integration to directly predict absolute free energies of solid and molten salts at any specified conditions of composition, temperature and pressure. This framework will combine a hierarchy of first-principles, molecular dynamics and continuum techniques to deliver first-principles-level accuracy at a fraction of the computational cost of conventional ab initio molecular dynamics approaches. In particular, this technique is expected to provide first-principles accuracy, while off-loading most of the computational work on much less expensive classical molecular dynamics and continuum techniques.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Considerations for a Medium-Voltage DC Electrolysis Testbed

Here we present the results of a study focused on the feasibility of using Medium Voltage DC (MVDC) power distribution from wind power generation to electrolyzers for hydrogen production. This approach, using hybrid energy generation in a MVDC microgrid, offers many advantages. These include possible improvements in efficiency, reliability and installation cost compared to a more typical state-of-the-art AC distribution configuration. It also eliminates the need for transformers, which have recently been subject to price volatility and availability concerns. This study highlights the practical feasibility of MVDC distribution networks for integrating various energy sources, offering improved efficiency and reduced system complexity compared to conventional AC-based solutions. Future work will focus on enhancing fault protection strategies, scaling the system to larger renewable installations, and conducting hardware implementation at the National Renewable Energy Laboratory's (NREL) Flatirons Campus (FC). In the sections that follow we show that a DC Collection and Distribution System (DC CDS) reduces the losses associated with the electrical conversion / distribution process relative to a state-of-the-art AC approach, improving overall efficiency by 5%. On the qualitative side, reducing the number of conversion stages is likely to improve reliability, reduce capital investment cost, and enable simpler control algorithms to be used, and reduced risk of instabilities and malfunctions.

08 HYDROGEN↗

NASA NTRS2011

Marshall Convergent Spray Formulation Improvement for High Temperatures

The Marshall Convergent Coating-1 (MCC-1) formulation was produced in the 1990s, and uses a standard bisphenol A epoxy resin system with a triamine accelerator. With the increasing heat rates forecast for the next generation of vehicles, higher-temperature sprayable coatings are needed. This work substitutes the low-temperature epoxy resins used in the MCC-1 coating with epoxy phenolic, epoxy novalac, or resorcinolinic resins (higher carbon content), which will produce a higher char yield upon exposure to high heat and increased glass transition temperature. High-temperature filler materials, such as granular cork and glass ecospheres, are also incorporated as part of the convergent spray process, but other sacrificial (ablative) materials are possible. In addition, the use of polyhedral oligomeric silsesquioxanes (POSS) nanoparticle hybrids will increase both reinforcement aspects and contribute to creating a tougher silacious char, which will reduce recession at higher heat rates. Use of expanding epoxy resin (lightweight MCC) systems are also useful in that they reduce system weight, have greater insulative properties, and a decrease in application times can be realized.

Scarpa, Jack↗

NASA NTRS2013

Verification of Numerical Programs: From Real Numbers to Floating Point Numbers

Numerical algorithms lie at the heart of many safety-critical aerospace systems. The complexity and hybrid nature of these systems often requires the use of interactive theorem provers to verify that these algorithms are logically correct. Usually, proofs involving numerical computations are conducted in the infinitely precise realm of the field of real numbers. However, numerical computations in these algorithms are often implemented using floating point numbers. The use of a finite representation of real numbers introduces uncertainties as to whether the properties veri ed in the theoretical setting hold in practice. This short paper describes work in progress aimed at addressing these concerns. Given a formally proven algorithm, written in the Program Verification System (PVS), the Frama-C suite of tools is used to identify sufficient conditions and verify that under such conditions the rounding errors arising in a C implementation of the algorithm do not affect its correctness. The technique is illustrated using an algorithm for detecting loss of separation among aircraft.

Goodloe, Alwyn E.↗

DOE OSTI2022

Control Oriented Model of Cabin-HVAC System in a Long-Haul Trucks for Energy Management Applications

Super Truck II is a 48V mild hybrid class 8 truck with an all auxiliary loads powered purely by the battery pack. Electric Heating Ventilation and Air Conditioning (HVAC) load is the most prominent battery load during the hotel period, when the truck driver is resting inside the sleeper. For the PACCAR Super Truck II (ST-II) project a 48 V battery system provides the required power during the hotel period. A cabin-HVAC model estimates the electric load on the 48V battery system, allowing the control system to implement an efficient energy management strategy that avoids engine idling during the hotel period. The thermal model accounts for the sun load due to the time of day and the geographic location of the truck during the hotel period. The cabin-HVAC model has two parts. First, a grey box model with two heat exchangers (Condenser and Evaporator) working in unison with refrigerant mass flow rate as an input and HVAC load as an output. Second, a two-node cabin model formulated to estimate the cabin temperature as a function of the Global Horizontal Irradiance (GHI), HVAC load and ambient temperature. The models are calibrated using experimental cabin-HVAC system data as for long-haul class 8 truck (e.g. ST-II). Here, the model simulations show that the overall Root Mean Square Error (RMSE) value of 0.4°C between the experimental and simulated cabin temperature.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2021

Analysis of Hybrid Gas–Dust Outbursts Observed at 67P/Churyumov–Gerasimenko

Cometary outbursts offer a valuable window into the composition of comet nuclei with their forceful ejection of dust and volatiles in explosive events, revealing the interior components of the comet. Understanding how different types of outbursts influence the dust properties and volatile abundances, to better interpret what signatures can be attributed to primordial composition and what features are the result of processing, is an important task best undertaken with a multi-instrument approach. The European Space Agency Rosetta mission to 67P/Churyumov–Gerasimenko carried a suite of instruments capable of carrying out this task in the near-nucleus coma with unprecedented spatial and spectral resolution. In this work, we discuss two outbursts that occurred 2015 November 7 and were observed by three instruments on board: the Alice ultraviolet spectrograph, the Visual Infrared and Thermal Imaging Spectrometer, and the Optical, Spectroscopic, and Infrared Remote Imaging System. Together, the observations show that mixed gas and dust outbursts can have different spectral signatures representative of their initiating mechanisms, with the first outburst showing indicators of a cliff collapse origin and the second more representative of fresh volatiles being exposed via a deepening fracture. This analysis opens up the possibility of remote spectral classification of cometary outbursts with future work.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2022

Use Cases and Model Development of Thermal Storage Coupling for Advanced Nuclear Reactors

This report discusses the different options for coupling thermal energy storage (TES) systems to advanced nuclear power plants (A-NPPs) in order to enable flexible and hybrid plant operation. An advanced light-water reactor (ALWR) and a high-temperature gas-cooled reactor (HTGR) were selected as the initial use cases for demonstrating a thermally balanced energy storage coupling design for thermal power extraction. Cost functions for the A-LWR were derived from the fully balanced models that were developed based on three different coupling options with three different thermal energy bypass ratios. For the next steps, cost functions for the HTGR will also be derived, and additional nuclear reactors (e.g., a liquid-cooled fast reactor [LFR] or molten-salt reactor [MSR]) will be evaluated for coupling with TES in similar fashion, including the evaluation of their steady-state condition models and cost functions. The models presented herein showcase several design considerations, focusing on optimal deployment methodologies for achieving steady-state operation with minimum disruption to the nuclear power generation cycle. This report presents the results of steady state models developed using Aspen HYSYS®, wherein the thermal energy bypass for an NPP-TES coupling was varied up to 50%. The various components were sized using Aspen Process Economic Analyzer (APEA) and Aspen Exchanger Design and Rating (EDR), when applicable. Cost functions from these models were developed using the latest publicly available data obtained from APEA V11. The current steady-state models and cost functions provide a baseline for additional work focusing on dynamic operation and process optimization by using Idaho National Laboratory (INL)’s Framework for Optimization of Resources and Economics (FORCE) tools to evaluate the technoeconomic viability and transient operations of TES-coupled A-NPPs.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS2017

A CFD Case Study of a Fan Stage with Split Flow Path Subject to Total Pressure Distortion Inflow

This report is the documentation of the work performed under the Hypersonic Project of the NASA's Fundamental Aeronautics Program. It was funded through Task Number NNC10E444T under GESS-2 Contract NNC06BA07B. The objective of the task is to develop advanced computational tools for the simulation of multi-stage turbomachinery in support of aeropropulsion. This includes work elements in extending the TURBO code and validating the multi-stage URANS (Unsteady Reynolds Averaged Navier Stokes) simulation results with the experimental data. The unsteady CFD (Computation Fluid Dynamics) calculations were performed in full wheel mode with and without screen generated total pressure distortion at the computational inflow boundary, as well as in single passage phase lag mode for uniform inflow. The experimental data were provided by NASA from the single stage RTA (Revolutionary Turbine Accelerator) fan test program.Significant non-uniform flow condition at the fan-face of the aeropropulsion system is frequentlyencountered in many of the advanced aerospace vehicles. These propulsion systems can be eithera podded or an embedded design employed in HWB (Hybrid Wing Body) airframe concept. It isalso a topic of interest in military applications, in which advanced air vehicles have already deployedsome form of embedded propulsion systems in their design because of the requirementsof compact and low observable inlets. Even in the conventional airframe/engine design, the fancould operate under such condition when the air vehicle is undergoing rapid maneuvering action.It is believed that a better understanding of the fan’s aerodynamic and aeromechanical responseto this type of operating condition or off design operation would be beneficial to designing distortiontolerant blades for improved engine operability.The objective for this research is to assess the capability of turbomachinery code as an analysistool in understanding the effects and evaluating the impact of flow distortion on the aerodynamicand aeromechanical performance of the fan in advanced propulsion systems. Results from thetesting of an advanced fan stage released by NASA are available and will be used here for CFDcode validation. The experiment was performed at NASA’s high speed compressor facility aspart of the RTA (Revolutionary Turbine Accelerator) demonstration project, a joint effort ofNASA Glenn Research Center and GE Aircraft Engines in developing an advanced Mach 4TBCC (Turbine Based Combined Cycle) turbofan/ramjet engine for access to space. Part of thetest was to assess the aerodynamic performance and operability of the fan stage under nonuniforminflow condition. Various flow distortion patterns were created at the fan-face by manipulatingsets of screens placed upstream of the wind tunnel. Measurements at the fan-face willprovide the necessary distortion flow information as the inflow boundary condition for the CFDin a full wheel simulation. Therefore the purpose of this work is to demonstrate the NASA supportedmulti-stage turbomachinery code, TURBO [1-5], in the aerodynamic performance analysisof a modern fan design operating under off design condition, and in particular to validate theCFD results with the RTA fan test data.A brief description of the RTA fan rig configuration is given in the next section, explaining onhow flow distortion were measured in the test and constructed for the CFD at the fan-face. It isfollowed by a section summarizing previous CFD work performed at NASA relevant to the currentfan configuration. A short description of the TURBO code is given next, followed by detailsin the computational model of the fan rig, the required computing resources, and the numericalprocedure for the simulations. The CFD results are presented in the discussion section and finallyconcluding remarks are summarized.

Fan Stage↗

DOE OSTI2026

Learning Latent Representations to Bridge Coarse-Grained and Atomistic Resolutions in Polymer Simulations

We present a machine-learning-based framework for learning reduced-order representations of polymer chain conformations across coarse-grained (CG) and united-atom (UA) fidelities. By employing linear singular value decomposition and nonlinear autoencoders, we compress high-dimensional polymer configurations into latent spaces with minimal loss of structural accuracy. Crucially, we demonstrate a near-perfect linear mapping between CG and UA latent spaces, enabling an efficient super-resolution back-mapping procedure that reconstructs high-fidelity UA configurations from CG simulations. While minor structural inaccuracies occur, they are effectively corrected through a brief molecular dynamics relaxation, forming a practical hybrid machine learning−physics scheme. This approach establishes the key structural prerequisites for accelerated polymer dynamics simulations: a compact and accurate latent encoding of polymer chain conformations and a validated multi-fidelity mapping that permits reconstruction of UA structures from CG configurations. The extension of this framework to explicit time evolution within the latent space, enabling dynamics to be propagated at CG fidelity and decoded to UA resolution only when required, represents a natural and well-motivated direction for future work.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Long-lived photoinduced polar states in metal halide perovskites

Ferroic polarization in hybrid perovskites is crucial for enhancing photovoltaic performance and developing potential electronic applications. Controlling ferroic polarization with an optical field enables probing of ferroic polarization without the unwanted interface ionic effects caused by electronic contacts. This study employs ultrafast near-infrared photoexcitation to control dynamic structural transitions in soft single crystalline hybrid Cu (II) halide perovskites, achieving a long-lived polar state (beyond 104 s) at room temperature. We probe reversible long-lived polar domains under near-infrared photoexcitation using in-situ second harmonic generation microscopy. Theoretical calculation informs the polar lattice microstrain likely induced by anisotropic structure deformation in octahedral copper halide under near-infrared photoexcitation. The reversible slow structure deformation is further confirmed by in-situ photo-induced X-ray diffraction measurement. This work provides a material platform for understanding, controlling, and probing polarization under photoexcitation. Our methodology enables the identification of previously undiscovered polar phases in ferroelectric halide perovskites.

Dou, Yixuan↗

DOE OSTI2024

Quantifying the thermal effect and methyl radical production in nanosecond repetitively pulsed glow discharges applied to a methane-air flame

In this work, we investigated non-equilibrium plasma produced by nanosecond repetitively pulsed glow discharges applied across a lean premixed methane-air flame. The flame is stationary, axisymmetric, and laminar. The discharges are applied on the symmetry axis crossing the reactant gases, flame front, and product gases, allowing phase-locked averaged measurements and comparisons with axisymmetric numerical simulations. The thermal effect and methyl radical production are quantified in the discharge in the reactant gas region. One-dimensional, two-beam, hybrid, femtosecond-picosecond, coherent anti-Stokes Raman scattering is used to acquire spatial and temporal profiles of temperature and oxygen-to-nitrogen concentration ratio. Photo-fragmentation laser-induced fluorescence is used to acquire quantitative two-dimensional profiles of methyl radicals in the discharge providing the first quantitative imaging of methyl produced ahead of a flame by plasma-induced methane dissociation. The spatial profiles of temperature and oxygen-to-nitrogen concentration ratio are in steady state, indicating that individual discharges have an insignificant heating effect. Upper and lower bounds of the produced mole fraction of methyl radicals in the plasma are obtained due to uncertainties in the collisional quenching rates of excited state methylidyne radicals in the plasma. The discharges produce a maximum of 600–1100 ppm of methyl radicals upstream of the flame front within 25 ns. This amount is similar to the predicted methyl mole fraction for the flame without plasma and thus represents a significant chemical perturbation to the reactants upstream of the flame front. The produced methyl follows an exponential decay in the first microsecond after the discharge with a decay constant of 8 µs close to the flame, and 0.8 µs further from the flame. The decay then deviates from the exponential curve and the methyl persists for tens of microseconds. The results suggest that for the tested configuration, the thermal effect of individual discharges through fast gas heating is negligible, while active chemical species are produced in large quantities in the reactant gases, upstream of the flame front.

hybrid fs-ps CARS↗

DOE OSTI2019

High Performance Perovskite-Based Solar Cells (Final Technical Report)

Hybrid lead-halide perovskite semiconductors have become one of the most heavily studied photovoltaic (PV) materials within the past ten years. However, these materials suffer from two key limitations that have ultimately limited the progression towards commercialization: (i) the inclusion of toxic lead (Pb) and (ii) instability towards moisture, oxygen, and temperature. This project has targeted the development of perovskite absorber materials that replace Pb with a benign alternative and that are stable under atmospheric conditions. Under this broad goal, the project had four major objectives: 1) Develop high-performance Pb-based PV devices and study alternative inorganic contact materials to improve the device stability; 2) Advance computational techniques to understand the electronic and optical properties of perovskite semiconductors from a theoretical perspective; 3) Explore various hybrid and inorganic halide, chalcohalide and chalcogenide perovskite absorbers as highly stable, Pb-free absorber alternatives; 4) Develop thin-film deposition and device fabrication methodologies to deposit high-quality Pb-free perovskite absorbers and high-performance devices. Within the first objective, the researchers fabricated high-performing methylammonium lead iodide solar cells based on both traditional architectures (using a TiO 2 contact) and inverted architectures using NiOx and novel CuCrO 2 as hole transport layers (HTL). The work with CuCrO 2 is the first work demonstrating CuCrO 2 as a promising contact material for future, stable perovskite solar cells. Towards the second objective researchers have calculated the intrinsic stability and optoelectronic properties of multiple Pb-free systems including chalcohalide (e.g. CsBiOF 2 ), halide (e.g. Cs 3 Sb 2 I 9 ), and chalcogenide perovskites (e.g. BaZr 1-x TixS 3 ). Additionally, the researchers have furthered the basic understanding of perovskite materials by introducing the concept of electronic dimensionality and its impact on optoelectronic properties. This understanding has had implications in PV applications and beyond. In the third and fourth objectives, the investigators have exhausted a myriad of Pb-free materials in search of a stable, promising Pb-free perovskite absorber, including chalochalides based on CsBiOF 2 , Pb-free halides (such as Cs 2 AgBiBr 6 , Cs 2 TiBr 6 , and Cs(Ge/Sn)I 3 ) , chalcogenide perovskites (e.g. BaZrS 3 ), and perovskite-related halides InI and silver bismuth iodide. While the researchers have studied many promising perovskites and perovskite-alternatives, a stable, high-performing Pb-free absorber has proven to be elusive.

14 SOLAR ENERGY↗