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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Property Evaluation and Damage Evolution of Environmental Barrier Coatings and Environmental Barrier Coated SiC/SiC Ceramic Matrix Composite Sub-Elements

This paper describes recent development of environmental barrier coatings on SiC/SiC ceramic matrix composites. The creep and fatigue behavior at aggressive long-term high temperature conditions have been evaluated and highlighted. Thermal conductivity and high thermal gradient cyclic durability of environmental barrier coatings have been evaluated. The damage accumulation and complex stress-strain behavior environmental barrier coatings on SiCSiC ceramic matrix composite turbine airfoil subelements during the thermal cyclic and fatigue testing of have been also reported.

Creep and fatigue↗
NASA NTRSDate not supplied

Influence of evaporation rate and chamber pressure on the FUV reflectance and physical characteristics of aluminum films

Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF2, or AlF3) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF2 coupons made by flash evaporation of aluminum followed by resistive evaporation of MgF2. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV reflectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF2 mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.

Manuel A. Quijada↗
NASA NTRSDate not supplied

Influence of Evaporation Rate and Chamber Pressure on the FUV Reflectance and Physical Characteristics of Aluminum Films

Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF2, or AlF3) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF2 coupons made by flash evaporation of aluminum followed by resistive evaporation of MgF2. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV reflectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF2 mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.

FUV reflectance, aluminum, PVD, deposition rate, A↗
NASA NTRSDate not supplied

Metal Contact Processing Experiments Towards Realizing 500 °C Durable RF 4H-SiC BJTs

This paper presents results from metal contact processing experiments towards the implementationof durable 500 deg.C high-frequency 4H-SiC bipolar junction transistors (BJTs). Specifically, p-type ohmic contacts have been demonstrated on a 0.25 μm-thick p-type homoepitaxial layer of doping 8 x 1018± 4 x 1018cm-3. Finally, preliminary current-voltage characteristics of fabricated BJTs are presented.

RF SiC↗
NASA NTRS2023

Metal Contact Processing Experiments Towards Realizing 500 °C Durable RF 4H-SiC BJTs

This paper presents results from metal contact processing experiments towards the implementation of durable 500 °C high-frequency 4H-SiC bipolar junction transistors (BJTs) . Specifically, p -type ohmic contacts have been demonstrated on a 0.25 μm-thick p -type homoepitaxial layer of doping 8 x 10 18 ± 4 x 10 18 cm -3 . Preliminary current-voltage characteristics of fabricated BJTs are presented.

4H-SiC BJT↗
DOE OSTI2026

Theory Guided Fine‐Tune of Strain Effects in Pt Ternary Alloy via Rare Earth Templating: Achieving High Performance PEMFCs Catalysts

The sluggish kinetics and insufficient durability of platinum-based catalysts remain crucial barriers limiting proton-exchange-membrane fuel cells (PEMFCs) deployment. Here, we report a theory-guided synthesis combined with rare-earth templating to realize a previously inaccessible Pt 5 Co-like phase with tailored atomic-scale strain. Guided by density functional theory (DFT) calculations, we identified that a Pt 5 Co-like sublayer can induce a unique mild compressive strain (−1.24%) to the Pt(111) shell and an optimal *OH binding energy shift (ΔE ≈ 0.11 eV). This shift positions the alloy catalyst near the apex of the oxygen reduction reaction activity volcano. This prediction guided the synthesis of ternary alloy Pt 5 (Ce)Co@Pt multilayer nanoparticles, featuring a Ce-stabilized core, a Pt 5 Co-like sublayer, and a Pt-rich shell. This catalyst demonstrates both exceptionally high activity and durability, achieving a mass activity of 2.6 A∙mg Pt −1 in rotating disk electrode testing. In fuel cell membrane electrode assembly tests, Pt 5 (Ce)Co@Pt achieves a current density of 1.9 A∙cm −2 at 0.7 V under heavy-duty vehicle conditions. Remarkably, it maintains 1.2 A∙cm −2 after 1 80 000 AST cycles, doubling the U.S. DOE 2025 target. This work demonstrates a rational design strategy that DFT-guided strain engineering integrates with rare-earth templating to advance Pt-based catalysts for fuel cell applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1992

Tribological evaluation of an Al2O3-SiO2 ceramic fiber candidate for high temperature sliding seals

A test program to determine the relative sliding durability of an alumina-silica candidate ceramic fiber for high temperature sliding seal applications as described. This work represents the first reporting of the sliding durability of this material system. Pin-on-disk tests were used to evaluate the potential seal material by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Friction was measured during the tests and fiber wear, indicated by the extent of fibers broken in the tow or bundle, was measured at the end of each test. Test variables studied included ambient temperatures from 25 C to 900 C, loads from 1.3 to 21.2 Newtons, and sliding velocities from 0.025 to 0.25 m/sec. In addition, the effects of fiber diameter, elastic modulus, and a pretest fiber heat treatment on friction and wear were measured. In most cases, wear increased with temperature. Friction ranged from about 0.36 at 500 C and low velocity (0.025 m/s) to over 1.1 at 900 C and high velocity (0.25 m/s). The pretest fiber heat treatment, which caused significant durability reductions for alumina-boria-silica ceramic fibers tested previously, had little effect on the alumina-silica fibers tested here. These results indicate that the alumina-silica (Al2O3-SiO2) fiber is a good candidate material system for high temperature sliding seal applications.

Dellacorte, Christopher↗
NASA NTRS1986

Simplified cyclic structural analyses of SSME turbine blades

Anisotropic high-temperature alloys are used to meet the safety and durability requirements of turbine blades for high-pressure turbopumps in reusable space propulsion systems. The applicability to anisotropic components of a simplified inelastic structural analysis procedure developed at the NASA Lewis Research Center is assessed. The procedure uses as input the history of the total strain at the critical crack initiation location computed from elastic finite-element analyses. Cyclic heat transfer and structural analyses are performed for the first stage high-pressure fuel turbopump blade of the space shuttle main engine. The blade alloy is directionally solidified MAR-M 246 (nickel base). The analyses are based on a typical test stand engine cycle. Stress-strain histories for the airfoil critical location are computed using both the MARC nonlinear finite-element computer code and the simplified procedure. Additional cases are analyzed in which the material yield strength is arbitrarily reduced to increase the plastic strains and, therefore, the severity of the problem. Good agreement is shown between the predicted stress-strain solutions from the two methods. The simplified analysis uses about 0.02 percent (5 percent with the required elastic finite-element analyses) of the CPU time used by the nonlinear finite element analysis.

Kaufman, A.↗
DOE OSTI2022

High-Platinum-Content Catalysts on Atomically Dispersed and Nitrogen Coordinated Single Manganese Site Carbons for Heavy-Duty Fuel Cells

Fuel cells for heavy-duty vehicles (HDVs) have attracted considerable attention because of their unique scalability, better fuel economy, the less demand for hydrogen refilling infrastructure. However, the potential application requires more stringent fuel cell durability up to 25,000 h. Membrane electrode assemblies (MEAs) made from platinum group metal (PGM) catalyst with relatively high loading 0.3 mgPt cm –2 play a crucial role in ensuring high-power and long-term durability. Integrating fine PGM nanoparticles and robust carbon support with strengthened interactions is critical for improving MEA performance and durability. Herein, a unique atomically dispersed and nitrogen coordinated single Mn site-rich carbon (M–N–C) support was developed for high content (40 wt%) platinum catalysts for the oxygen reduction reaction (ORR) cathode with reduced thickness. Compared with two controls studied in this work (e.g., a porous graphitic carbon-supported Pt and a commercial TKK Pt/C catalysts), the Pt (40 wt%)/Mn–N–C catalyst exhibited much enhanced catalytic activity and stability for the ORR in both aqueous acidic electrolyte and polymer electrolyte-based MEA. Here, we carefully elucidated the—role of the Mn–N–C support in promoting Pt catalyst concerning its high surface area, partially graphitic structure, and nitrogen dopants, providing better Pt nanoparticle dispersion, and strengthened interactions between Pt and carbon. Consequently, the MEA from the Pt (40 wt%)/Mn–N–C catalyst generated a 1.61 A cm –2 at 0.7 V based on HDV conditions (0.2 mgPt cm –2 and 250 kPa air). More importantly, the MEA is highly durable and can retain 1.31 A cm –2 at 0.7 V after 30,000 voltage cycles (~19% loss), surpassing the commercial Pt/C catalyst (loss of ~56%). Therefore, the Mn–N–C carbon-supported Pt catalyst holds a great promise to meet the challenging DOE target (1.07 A cm –2 at 0.7 V after 150,000 cycles) for HDVs.

25 ENERGY STORAGE↗
NASA NTRS1999

Thermomechanical Fatigue Durability of T650-35/PMR-15 Sheet-Molding Compound Evaluated

High-performance polymer matrix composites (PMC's) continue to be the focus of a number of research efforts aimed at developing cost-effective, lightweight material alternatives for advanced aerospace and aeropropulsion applications. These materials not only offer significant advantages in specific stiffness and strength over their current metal counterparts, but they can be designed and manufactured to eliminate joints and fasteners by combining individual components into integral subassemblies, thus making them extremely attractive for commercial applications. With much emphasis on the low-cost manufacturing aspects of advanced composite structures, there is heightened interest in high-performance sheet-molding compounds (SMC's). Researchers at the NASA Lewis Research Center, in cooperation with the Allison Advanced Development Company, completed an investigation examining the use of T650-35/PMR-15 SMC for a midstage inner-vane endwall application within a gas turbine engine compressor. This component resides in the engine flow path and is subjected not only to high airflow rates, but also to elevated temperatures and pressures. This application is unique in that it represents a very aggressive use of high-performance SMC's, raising obvious concerns related to durability and property retention in the presence of microstructural damage. Therefore, it was necessary to evaluate the fatigue behavior and damage tolerance of this material subjected to a representative thermomechanical fatigue (TMF) mission-cycle loading spectrum.

Castelli, Michael G.↗
DOE OSTI2026

Nonenergy Biomass Carbon Removal and Storage (BiCRS): Assessing Durability of Nongaseous Carbon Products Across Terrestrial Storage Fates

Biomass Carbon Removal and Storage, or BiCRS, pathways use plants or algae that remove carbon dioxide from the atmosphere through photosynthesis and store it underground or in long-lived products. While some BiCRS approaches generate an energy product, all BiCRS approaches generate a carbon product. A new subset of BiCRS approaches focus on the storage of these raw or converted carbon products for generation of carbon credits. However, the durability of these approaches is highly variable as carbon products vary widely in their “form” and the conditions of their “fate.” We organize our thinking about carbon products and their durability around these two primary axes. The durability of carbon product “forms” is mediated by chemical recalcitrance and ranges substantially across agricultural residues, municipal solid waste, woody biomass, and nongaseous products of thermochemical conversion (e.g., biochars and bio-oils). Meanwhile, terrestrial storage “fates” vary in the mechanism employed to stall decay, including surface storage, dry storage, shallow anoxic storage, and deep or geologic anoxic storage (or injection). Each mechanism has different implications for suitability with different feedstock forms as well as long-term risks. We present a framework for assessing durability of solid or liquid raw and conversion carbon products under terrestrial storage fates, highlighting knowns, unknowns, and research priorities moving forward.

09 BIOMASS FUELS↗
NASA NTRS2008

Advanced Low Conductivity Thermal Barrier Coatings: Performance and Future Directions (Invited paper)

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. In this presentation, thermal barrier coating development considerations and performance will be emphasized. Advanced thermal barrier coatings have been developed using a multi-component defect clustering approach, and shown to have improved thermal stability and lower conductivity. The coating systems have been demonstrated for high temperature combustor applications. For thermal barrier coatings designed for turbine airfoil applications, further improved erosion and impact resistance are crucial for engine performance and durability. Erosion resistant thermal barrier coatings are being developed, with a current emphasis on the toughness improvements using a combined rare earth- and transition metal-oxide doping approach. The performance of the toughened thermal barrier coatings has been evaluated in burner rig and laser heat-flux rig simulated engine erosion and thermal gradient environments. The results have shown that the coating composition optimizations can effectively improve the erosion and impact resistance of the coating systems, while maintaining low thermal conductivity and cyclic durability. The erosion, impact and high heat-flux damage mechanisms of the thermal barrier coatings will also be described.

Zhu, Dongming↗
NASA NTRS2008

Advanced Low Conductivity Thermal Barrier Coatings: Performance and Future Directions

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. In this presentation, thermal barrier coating development considerations and performance will be emphasized. Advanced thermal barrier coatings have been developed using a multi-component defect clustering approach, and shown to have improved thermal stability and lower conductivity. The coating systems have been demonstrated for high temperature combustor applications. For thermal barrier coatings designed for turbine airfoil applications, further improved erosion and impact resistance are crucial for engine performance and durability. Erosion resistant thermal barrier coatings are being developed, with a current emphasis on the toughness improvements using a combined rare earth- and transition metal-oxide doping approach. The performance of the toughened thermal barrier coatings has been evaluated in burner rig and laser heat-flux rig simulated engine erosion and thermal gradient environments. The results have shown that the coating composition optimizations can effectively improve the erosion and impact resistance of the coating systems, while maintaining low thermal conductivity and cyclic durability. The erosion, impact and high heat-flux damage mechanisms of the thermal barrier coatings will also be described.

Zhu, Dongming↗
DOE OSTI2020

GeoMelt{sup R} In-Container Vitrification (ICV){sup TM} for Fukushima Daiichi Water Treatment Secondary Wastes - 20212

The Japanese government is supporting development work implemented jointly by Veolia subsidiaries Kurion Japan, K.K., Veolia Nuclear Solutions (VNS), Inc., and Veolia Nuclear Solutions Federal Services, LLC for treating radioactive waste generated from Fukushima Daiichi Nuclear Power Station (NPS) water treatment using the GeoMelt{sup TM} In-Container Vitrification (ICV){sup TM} technology. The initial work consisted of glass formulation and engineering-scale testing which was completed in 2018, in the frame of an IRID (International Research Institute for Nuclear Decommissioning) program as part of a project subsidized by Japan's Ministry of Economy, Trade and Industry (METI). The Fukushima Daiichi NPS Mid- and Long-Term Road-map requires investigation of methods to stabilize solid wastes (and to immobilize radioisotopes in the wastes) generated as a result of emergency response and decommissioning activities. Cooling water treatment has resulted in a significant amount of solid and slurry secondary wastes (mostly adsorbents and ion-exchange materials) which will require processing at some point. GeoMelt{sup R} ICV{sup TM} is a joule-heated melter technology which uses a refractory-lined single-use container combining the melter and disposal container. There is no pouring required nor concerns with refractory corrosion which allows the process to accommodate a wide range of waste chemistries and high waste loadings. The testing described here consisted of three engineering-scale melts, each processing between 212 kg and 240 kg of waste simulants, glass formers, and non-radioactive cesium (Cs) and strontium (Sr) tracers. Continuous isokinetic stack sampling of off-gas emissions was performed for each test in order to calculate Cs and Sr retention in the glass wasteform. Single-pass retention of Cs in the final glass wasteform ranged from 91.46 to 99.30%, and single-pass retention of Sr ranged from 99.76 to 100%. Planned particulate recycle will increase these retention levels. Melt 1 processed a mixture of KUR-EH (a zeolite-based ion-exchange material), simulated Advanced Liquid Processing System (ALPS) Carbonate and Iron Slurries, and glass additives. Melt 2 processed a mixture of KUR-EH, KUR-TSG (a titanate-based adsorbent), and glass additives. Melt 3 processed a mixture of KUR-EH, simulated barium sulfate/iron ferrocyanide sludge (AREVA sludge), and glass additives. Waste loadings for these melts ranged from 70 weight percent (wt%) to 82 wt%. Vitrification produces a waste form much denser than the stored water treatment secondary waste wastes, resulting in significant volume reduction. Volume reductions for the three tests ranged from 74 to 79 vol%. Vitrification produces a chemically durable wasteform. Pacific Northwest National Laboratory (PNNL) tested three glass samples from each engineering-scale melt) by the Materials Characterization Center 1 (MCC-1) test, an international standard leach test of the chemical durability of nuclear waste glasses. PNNL also obtained one U.S. reference glass (EA Glass) and two Japan reference glasses P0798) and tested these under the same MCC-1 conditions (90 deg. C, 10 m-1, DIW, and 7, 14, 28-day) as the GeoMelt{sup R} ICV{sup TM} glasses. The GeoMelt{sup R} ICV{sup TM} glasses exhibited lower total normalized releases and 14- to 28-day normalized release rates than the three reference glasses. These results suggest that the GeoMelt{sup R} ICV{sup TM} glasses have durabilities on par with high-level waste glasses under standard test conditions. Post-melt process sampling and analysis indicated no Cs migration into the melter refractory materials and very little deposition of Cs or Sr onto the melter hood or off-gas piping internals. The results of the testing indicated good Cs retention in the glass, high volume reduction and waste loadings, and excellent chemical durability. These factors are important to minimize treatment costs and to protect workers and the environment. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Environmentally Friendly Use of Carbon Ore for Advanced Building Materials for Homes and Commercial Buildings

Through this effort, X-MAT CCC sought to confirm the utility and commercialization potential of carbon-derived building materials (CDBM) technology licensed from our partner, Semplastics. These CDBM products contain at least 52% coal-derived carbon by mass. Including the binders within the resin, the products contain at least 71% carbon by mass overall, meeting a key criterion for DE-FOA-0002185 – Area of Interest (AOI) 5 – Design Research and Development, Validation, and Fabrication of a Prototype Carbon-Based Building. The Phase II project has resulted in a technology demonstrator prototype structure, a detailed design for a carbon-based building, and updated techno-economic analysis (TEA) including detailed market surveys to show the commercial viability of CDBM products. We pursued the following objectives in Phase II: (1) construction of a partial building shell as a technology demonstrator, (2) testing of CDBM products, individually and in assemblies, (3) demonstration of bonding of CDBM and traditional building materials (TBM) in structural applications, (4) production of a detailed design for a carbon-based building, and (5) an update of the TEA that was performed in Phase I. In Phase II, X-MAT CCC and our industry team performed the development and testing needed to improve the maturity of the technology from a Technology Readiness Level (TRL) of 5 to TRL 6. CDBM have been shown by our partner Semplastics to exhibit a number of high-performance characteristics, including high strength (five times the flexure strength of the best commercial brick, and more than twice the compressive strength of construction-grade concrete block), lower density, improved mechanical durability and abrasion resistance, very high temperature stability, and resistance to chemicals, acids, salts, and water. These properties offer significant improvements over conventional building materials. Phase II built upon the work accomplished in Phase I by performing technical and economic research and development to confirm the viability of CDBM as commercial products in various markets. Acknowledgment: This material is based upon work supported by the Department of Energy under Award Number DE-FE0031985.

01 COAL, LIGNITE, AND PEAT↗
NASA NTRS2006

Engine Development Design Margins Briefing Charts

New engines experience durability problems after entering service. The most prevalent and costly is the hot section, particularly the high-pressure turbine. The origin of durability problems can be traced back to: 1) the basic aero-mechanical design systems, assumptions, and design margins used by the engine designers, 2) the available materials systems, and 3) to a large extent, aggressive marketing in a highly competitive environment that pushes engine components beyond the demonstrated capability of the basic technology available for the hardware designs. Unfortunately the user must operate the engine in the service environment in order to learn the actual thrust loading and the time at max effort take-off conditions used in service are needed to determine the hot section life. Several hundred thousand hours of operational service will be required before the demonstrated reliability of a fleet of engines or the design deficiencies of the engine hot section parts can be determined. Also, it may take three to four engine shop visits for heavy maintenance on the gas path hardware to establish cost effective build standards. Spare parts drive the oerator's engine maintenance costs but spare parts also makes lots of money for the engine manufacturer during the service life of an engine. Unless competition prevails for follow-on engine buys, there is really no motivation for an OEM to spend internal money to improve parts durability and reduce earnings derived from a lucrative spare parts business. If the hot section life is below design goals or promised values, the OEM migh argue that the engine is being operated beyond its basic design intent. On the other hand, the airframer and the operator will continue to remind the OEM that his engine was selected based on a lot of promises to deliver spec thrust with little impact on engine service life if higher thrust is used intermittently. In the end, a standoff prevails and nothing gets fixed. This briefing will propose ways to hold competing engine manufacturers more accountable for engine hot section design margins during the entire Engine Development process as well as provide tools to assess the design temperature margins in the hot section parts of Service Engines.

Bentz, Chuck↗
NASA NTRS2005

Crack Driving Forces in a Multilayered Coating System for Ceramic Matrix Composite Substrates

The effects of the top coating thickness, modulus and shrinkage strains on the crack driving forces for a baseline multilayer Yttria-Stabilized-Zirconia/Mullite/Si thermal and environment barrier coating (TEBC) system for SiC/SiC ceramic matrix composite substrates are determined for gas turbine applications. The crack driving forces increase with increasing modulus, and a low modulus thermal barrier coating material (below 10 GPa) will have no cracking issues under the thermal gradient condition analyzed. Since top coating sintering increases the crack driving forces with time, highly sintering resistant coatings are desirable to maintain a low tensile modulus and maintain a low crack driving force with time. Finite element results demonstrated that an advanced TEBC system, such as ZrO2/HfO2, which possesses improved sintering resistance and high temperature stability, exhibited excellent durability. A multi-vertical cracked structure with fine columnar spacing is an ideal strain tolerant coating capable of reducing the crack driving forces to an acceptable level even with a high modulus of 50 GPa.

Ghosn, Louis J.↗
DOE OSTI2021

Perovskite Solar Cells Go Bifacial—Mutual Benefits for Efficiency and Durability

Bifacial solar cells hold the potential to achieve a higher power output per unit area than conventional monofacial devices without significantly increasing manufacturing costs. However, efficient bifacial designs are challenging to implement in inorganic thin-film solar cells because of their short carrier lifetimes and high rear surface recombination. The emergence of perovskite photovoltaic (PV) technology creates a golden opportunity to realize efficient bifacial thin-film solar cells, owing to their outstanding optoelectronic properties and unique features of device physics. More importantly, transparent conducting oxide electrodes can prevent electrode corrosion by halide ions, mitigating one major instability issue of the perovskite devices. Here, the theory of bifacial PV devices is summarized and the advantages of bifacial perovskite solar cells, such as high power output, enhanced device durability, and low economic and environmental costs, are reviewed. The limitations and challenges for bifacial perovskite solar cells are also discussed. Lastly, the awareness of bifacial solar cells as a feasible commercialization pathway of perovskite PV for mainstream solar power generation and building-integrated PV is advocated and future research directions are suggested.

14 SOLAR ENERGY↗