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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Importance of Reducing Vapor Atmosphere in the Fabrication of Tin-Based Perovskite Solar Cells

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the tendency of these materials to form leakage pathways from p-type defect states, mainly Sn 4+ and Sn vacancies, causes poor device reproducibility and limits the overall power conversion efficiencies. Here, we present an effective process that involves a reducing vapor atmosphere during the preparation of tin-based halide perovskite solar cells to solve this problem, using MASnI 3 , CsSnI 3 and CsSnBr 3 as the representative absorbers. This process enables the fabrication of remarkably improved solar cells with power conversion efficiencies of 3.89%, 1.83% and 3.04% for MASnI 3 , CsSnI 3 and CsSnBr 3 respectively. The reducing vapor atmosphere process results in more than 20% reduction of Sn 4+ /Sn 2+ ratios, which leads to greatly suppressed carrier recombination, to a level comparable to their lead-based counterparts. These results mark an important step towards a deeper understanding of the intrinsic tin-based halide perovskite materials, paving the way to the realization of low-cost and lead-free Sn-based halide perovskite solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Fabrication of high efficiency perovskite solar cells based on mesoporous TiO2 nanofibrous film under high humidity conditions

Highlights: • 1D TiO{sub 2} nanofibrous film was prepared by electrospinning technique as mesoporous of PSCs. • PSCs were fabricated under ambient conditions even with a high humidity condition more than 40%. • The 1D TiO{sub 2} nanofiber-based PSCs achieved a power conversion efficiency (PCE) about 11.6% compared with 7.5% whereas the 0D TiO{sub 2} nanoparticle-based PSCs only has 7.5%. - Abstract: One-dimensional (1D) TiO{sub 2} nanofibrous film with good morphology and electrical characteristics was prepared by electrospinning technique. And then perovskite solar cells (PSCs) were fabricated based on 2-μm-thick mesoporous TiO{sub 2} nanofibrous film under ambient conditions even with a high humidity condition more than 40%. The devices show high power conversion efficiency (PCE) due to high porosity that is beneficial to the loading of CH{sub 3}NH{sub 3}PbI{sub 3} perovskite layer. This high-porosity 1D TiO{sub 2} nanofibrous film also acts as a protection layer which can enhance the moisture stability of CH{sub 3}NH{sub 3}PbI{sub 3}. As a result, conversion efficiency of 11.6% and short-circuit current density (J{sub sc}) of 17.3 mA were achieved under 100 mW cm{sup −2} AM 1.5 G solar illumination. These two values are both higher than those of zero-dimensional (0D) TiO{sub 2} nanoparticulate film-based devices.

14 SOLAR ENERGY↗
DOE OSTI2015

Synthesis of self-detached nanoporous titanium-based metal oxide

In this study, self-detached nanoporous titanium-based metal oxide was synthesized for the first time by ultrafast anodization in a fluoride-free electrolyte containing 10% HNO{sub 3}. The nanoporous oxide has through-holes with diameters ranging from 10 to 60 nm. The as-formed oxides are amorphous, and were transformed to crystalline structures by annealing. The performance of a dye sensitized solar cell using nanoporpous Ti–10Zr oxide (TZ10) was further studied. It was found that the TZ10 film could increase both the short-circuit current and the open-circuit photovoltage of the solar cell. The overall efficiency of the solar cell was 6.99%, an increase of 20.7% as compared to that using a pure TiO{sub 2} (P25) film. - Graphical abstract: The nanoporous Ti–xZr(x=10, 30) oxide layers are fabricated by anodizing in a dilute nitric acid solvent. The power conversion efficiency of the DSSC by a covering of a Ti–10Zr thin film is increased by 20.7%, with an η of 7.69% , a short circuit current of 12.4 mA/cm{sup 2}, a open circuit voltage of 0.833 V, and a fill factor of 0.679. - Highlights: • Self-detached nanoporous titanium-based metal (TiZr) oxide was synthesized. • The TiZr oxides have through-hole nanopores with diameters ranging from 10 to 60 nm. • The nanoporous Ti–10Zr oxide can improve the power conversion efficiency of a DSSC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Reduced defect density at the CZTSSe/CdS interface by atomic layer deposition of Al{sub 2}O{sub 3}

The greatest challenge for improving the power conversion efficiency of Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe)/CdS/ZnO thin film solar cells is increasing the open circuit voltage (V{sub OC}). Probable leading causes of the V{sub OC} deficit in state-of-the-art CZTSSe devices have been identified as bulk recombination, band tails, and the intertwined effects of CZTSSe/CdS band offset, interface defects, and interface recombination. In this work, we demonstrate the modification of the CZTSSe absorber/CdS buffer interface following the deposition of 1 nm-thick Al{sub 2}O{sub 3} layers by atomic layer deposition (ALD) near room temperature. Capacitance-voltage profiling and quantum efficiency measurements reveal that ALD-Al{sub 2}O{sub 3} interface modification reduces the density of acceptor-like states at the heterojunction resulting in reduced interface recombination and wider depletion width. Indications of increased V{sub OC} resulting from the modification of the heterojunction interface as a result of ALD-Al{sub 2}O{sub 3} treatment are presented. These results, while not conclusive for application to state-of-the-art high efficiency CZTSSe devices, suggest the need for further studies as it is probable that interface recombination contributes to reduced V{sub OC} even in such devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Carbazole-Based Hole-Transport Materials for High-Efficiency and Stable Perovskite Solar Cells

As organic–inorganic halide perovskite solar cells (PSCs) near commercialization, stability challenges during real-world conditions, such as durability at elevated temperatures, still need to be addressed. We have previously reported that doping of triarylamine-based hole-transport layers (HTLs) with a triarylamine-based radical cation salt (EHCz-3EtCz/EH44-ox) leads to enhanced PSC stability at elevated temperatures. While it was shown the radical cation dopant did not need to be identical to the HTL matrix, little was known about dopant exchange to realize the maximum impact on device-level properties (e.g., increase in low intrinsic conductivity, mobility, hydrophobic properties, ease of synthesis, and thermal stability). In this paper, we study the impact of dopant exchange among stable, low-cost, high-glass-transition temperature (Tg), and easily synthesized triarylamine-based HTL and radical triarylamine cation salts as dopants. Using EH44-ox as dopant leads to the improved device-level power conversion efficiency (PCE) for all HTL matrices assessed. Moreover, increasing the number of ethylhexyl chains from one to two per molecule and positioning these chains at the periphery rather than the core resulted in improved hydrophobicity. PSCs based on our HTL formulations have similar power conversion efficiencies (PCE) as those of PSCs based on commercially available HTLs while demonstrating greatly improved device-level stability at elevated temperatures.

14 SOLAR ENERGY↗
DOE OSTI2023

Near-infrared absorbing acceptor with suppressed triplet exciton generation enabling high performance tandem organic solar cells

Reducing the energy loss of sub-cells is critical for high performance tandem organic solar cells, while it is limited by the severe non-radiative voltage loss via the formation of non-emissive triplet excitons. Herein, we develop an ultra-narrow bandgap acceptor BTPSeV-4F through replacement of terminal thiophene by selenophene in the central fused ring of BTPSV-4F, for constructing efficient tandem organic solar cells. The selenophene substitution further decrease the optical bandgap of BTPSV-4F to 1.17 eV and suppress the formation of triplet exciton in the BTPSV-4F-based devices. The organic solar cells with BTPSeV-4F as acceptor demonstrate a higher power conversion efficiency of 14.2% with a record high short-circuit current density of 30.1 mA cm –2 and low energy loss of 0.55 eV benefitted from the low non-radiative energy loss due to the suppression of triplet exciton formation. We also develop a high-performance medium bandgap acceptor O1-Br for front cells. By integrating the PM6:O1-Br based front cells with the PTB7-Th:BTPSeV-4F based rear cells, the tandem organic solar cell demonstrates a power conversion efficiency of 19%. The results indicate that the suppression of triplet excitons formation in the near-infrared-absorbing acceptor by molecular design is an effective way to improve the photovoltaic performance of the tandem organic solar cells.

14 SOLAR ENERGY↗
DOE OSTI2018

Designing High-Efficiency Thin Silicon Solar Cells Using Parabolic-Pore Photonic Crystals

We demonstrate the efficacy of wave-interference-based light trapping and carrier transport in parabolic-pore photonic-crystal, thin-crystalline silicon (c -Si) solar cells to achieve above 29% power conversion efficiencies. Using a rigorous solution of Maxwell’s equations through a standard finite-difference time domain scheme, we optimize the design of the vertical-parabolic-pore photonic crystal (PhC) on a 10 μm -thick (c -Si) solar cell to obtain a maximum achievable photocurrent density (MAPD) of 40.6 mA/cm 2 beyond the ray-optical, Lambertian light-trapping limit. For a slanted-parabolic-pore PhC that breaks x-y symmetry, improved light trapping occurs due to better coupling into parallel-to-interface refraction modes. We achieve the optimum MAPD of 41.6 mA/cm 2 for a tilt angle of 10° with respect to the vertical axis of the pores. This MAPD is further improved to 41.72 mA/cm 2 by introducing a 75-nm SiO 2 antireflective coating on top of the solar cell. We use this MAPD and the associated charge-carrier generation profile as input for a numerical solution of Poisson’s equation coupled with semiconductor drift-diffusion equations using a Shockley-Read-Hall and Auger recombination model. Using experimentally achieved surface recombination velocities of 10 cm/s, we identify semiconductor doping profiles that yield power conversion efficiencies over 29%. Practical considerations of additional upper-contact losses suggest efficiencies close to 28%. This improvement beyond the current world record is largely due to an open-circuit voltage approaching 0.8 V enabled by reduced bulk recombination in our thin silicon architecture while maintaining a high short-circuit current through wave-interference-based light trapping.

14 SOLAR ENERGY↗
DOE OSTI2023

Efficient and stable perovskite solar cells based on blade-coated CH 3 NH 3 PbI 3 thin films fabricated using “green” solvents under ambient conditions

Metal halide perovskites are considered the most promising candidates for solar cells of the decade due to their exceptional optical and electronic properties. The power conversion efficiency of metal halide perovskites, when incorporated as the active layer of solar cells, has become comparable to that observed for conventional silicon solar cells. However, the stability, scaleup, green solvent usage, and fabrication in ambient conditions of metal halide perovskites need to be solved for commercial applications. Here, in this work, we report the fabrication of blade-coated methylammonium lead iodide (MAPbI 3 ) perovskite thin films using methylamine and acetonitrile as “green” solvents under ambient conditions. Our perovskite films are initially prepared from low purity PbI2 (99%) and are blade-coated in dry air at relative humidity (RH) levels above 30%. A significant advantage of fabricating our perovskite thin films via blade-coating protocols is that there is a minimal amount of precursors (5 μL) used compared to spin-coating methods (50μL–60μL) for a 4 cm 2 substrate. With the addition of a small amount of an organic halide salt, namely, phenethylammonium chloride, the film crystallinity is improved and non-radiative recombination is suppressed, resulting in power conversion efficiencies over 20%. In addition, the device maintains more than 95% of its initial efficiency after 500 h under continuous light illumination of 1-sun at open circuit conditions, 50 °C and 60% RH. The above method leads a path towards the commercial fabrication of perovskite solar cells.

14 SOLAR ENERGY↗
DOE OSTI2018

Near-Infrared Ternary Tandem Solar Cells

The paucity of near-infrared (NIR) organic materials with high absorption at long wavelengths, combined with large diffusion lengths and charge mobilities, is an impediment to progress in achieving high-efficiency organic tandem solar cells. Here a subcell is employed within a series tandem stack that comprises a solution-processed ternary blend of two NIR-absorbing nonfullerene acceptors and a polymer donor combined with a small-molecular-weight, short-wavelength fullerene-based subcell grown by vacuum thermal evaporation. Additionally, the ternary cell achieves a power conversion efficiency of 12.6 ± 0.3% with a short-circuit current of 25.5 ± 0.3 mA cm -2 , an open-circuit voltage of 0.69 ± 0.01 V, and a fill factor of 0.71 ± 0.01 under 1 sun, AM 1.5G spectral illumination. The success of this device is a result of the nearly identical offset energies between the lowest unoccupied molecular orbitals (LUMOs) of the donors with the highest occupied molecular orbital (HOMO) of the acceptor, resulting in a high open-circuit voltage. A tandem structure with an antireflection coating combining these subcells demonstrates a power conversion efficiency of 15.4 ± 0.3%.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Light-trapping in perovskite solar cells

We numerically demonstrate enhanced light harvesting efficiency in both CH{sub 3}NH{sub 3}PbI{sub 3} and CH(NH{sub 2}){sub 2}PbI{sub 3}-based perovskite solar cells using inverted vertical-cone photonic-crystal nanostructures. For CH{sub 3}NH{sub 3}PbI{sub 3} perovskite solar cells, the maximum achievable photocurrent density (MAPD) reaches 25.1 mA/cm{sup 2}, corresponding to 92% of the total available photocurrent in the absorption range of 300 nm to 800 nm. Our cell shows 6% absorption enhancement compared to the Lambertian limit (23.7 mA/cm{sup 2}) and has a projected power conversion efficiency of 12.9%. Excellent solar absorption is numerically demonstrated over a broad angular range from 0 to 60 degree for both S- and P- polarizations. For the corresponding CH(NH{sub 2}){sub 2}PbI{sub 3} based perovskite solar cell, with absorption range of 300 nm to 850 nm, we find a MAPD of 29.1 mA/cm{sup 2}, corresponding to 95.4% of the total available photocurrent. The projected power conversion efficiency of the CH(NH{sub 2}){sub 2}PbI{sub 3} based photonic crystal solar cell is 23.4%, well above the current world record efficiency of 20.1%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Metal oxide barrier layers for terrestrial and space perovskite photovoltaics

Perovskite photovoltaics are attractive for both terrestrial and space applications. Although terrestrial conditions require durability against stressors such as moisture and partial shading, space poses different challenges: radiation, atomic oxygen, vacuum and high-temperature operation. Here we demonstrate a silicon oxide layer that hardens perovskite photovoltaics to critical space stressors. A 1-um-thick silicon oxide layer evaporated atop the device contacts blocks 0.05 MeV protons at fluences of 10 15 cm -2 without a loss in power conversion efficiency, which results in a device lifetime increase in low Earth orbit by x20 and in highly elliptical orbit by x30. Silicon-oxide-protected Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 ) (MA, methylammonium; FA, formamidinium cation) and CsPbI 2 Br cells survive submergence in water and N,N-dimethylformamide. Furthermore, moisture tolerance of Sn-Pb and CsPbI 2 Br devices is boosted. Devices are also found to retain power conversion efficiencies on exposure to alpha irradiation and atomic oxygen. So, this barrier technology is a step towards lightweight packaging designs for both space and terrestrial applications.

14 SOLAR ENERGY↗
DOE OSTI2018

Enhanced efficiency of large-area dye-sensitized solar cells by light-scattering effect using multilayer TiO2 photoanodes

Highlights: • DSSCs with an active area of 100.6 cm{sup 2} and light-scattering layers are fabricated. • The light-scattering effect is shown to enhance the light absorption in the red part of the solar spectrum. • The light-scattering effect is more important than the dye adsorption capacity for TiO{sub 2} photoanodes with same thickness. • The highest power conversion efficiency of 7.52% has been obtained by the DSSC with optimized conditions. - Abstract: In order to reduce the usage of photoactive dye and improve light harvesting by the photoanode of dye-sensitized solar cells (DSSCs), TiO{sub 2} scatting layers were introduced. We have investigated the light-scattering effect in large-area DSSCs with an active area of 100.6 cm{sup 2} that contain diffusing or reflective layers. The result shows that the light-scattering effect is more important than the dye adsorption capacity for the light harvesting property of TiO{sub 2} photoanodes with same thickness, and the light-scattering effect is shown to enhance the light absorption in the red part of the solar spectrum. The highest power conversion efficiency of 7.52% has been obtained by the cell with optimized high dye adsorption layer and high light-scattering layer, which is 9.5% higher than that of the cell without the light-scattering layer (6.87%).

14 SOLAR ENERGY↗
DOE OSTI2022

A New Low-Temperature Approach for Efficient and Low-Cost Group V Doping in CdTe Thin Film Solar Cells (Final Technical Report)

The goal of this project is to develop a highly efficient low-temperature ex-situ Group V diffusion doping approach in the CdCl 2 treated polycrystalline CdTe film using the group V chlorides (i.e., PCl 3 , AsCl 3 , SbCl 3 , and BiCl 3 ) as dopants source. For the first time, our innovative doping strategies through the low-temperature ex-situ Group V doping process in polycrystalline CdSeTe successfully demonstrated a promising power conversion efficiency of ~19% compared to the Cu-doped counterparts. Our newly developed low-temperature ex-situ group V doping allows dedicated control of group V diffusion amount, generates a desirable depth profile, and is completely compatible with commercial CdTe module manufacturing. We built the partnership with the largest CdTe solar module manufacturing in the US, e.g., First Solar, Inc to further develop these low-temperature diffusion doped CdSeTe solar cells. Our technology was granted US Patent No. US11257977B2. In this project, we systematically investigate and characterize the new ex-situ group V doping mechanisms, defect chemistry, microstructure, and device physics in CdTe solar cells by combining experimental and theoretical means to pave the way to achieve lower cost toward $\$$0.02/kWh and higher power conversion efficiency (PCE) toward 25% in polycrystalline CdTe solar technology. This project will benefit the public by providing more affordable solar electricity and provide an effective way to address climate change.

14 SOLAR ENERGY↗
DOE OSTI2021

Investigating anode off-gas under spark-ignition combustion for SOFC-ICE hybrid systems

Solid oxide fuel cell – internal combustion engine (SOFC-ICE) hybrid systems are an attractive solution for electricity generation. The system can achieve up to 70% theoretical electric power conversion efficiency through energy cascading enabled by utilizing the anode off-gas from the SOFC as the fuel source for the ICE. Experimental investigations were conducted with a single cylinder Cooperative Fuel Research (CFR) engine by altering fuel-air equivalence ratio (φ), and compression ratio (CR) to study the engine load, combustion characteristics, and emissions levels of dry SOFC anode off-gas consisting of 33.9% H 2 , 15.6% CO, and 50.5% CO 2 . The combustion efficiency of the anode off-gas was directly evaluated by measuring the engine-out CO emissions. The highest net-indicated fuel conversion efficiency of 31.3% occurred at φ = 0.90 and CR = 13:1. These results demonstrate that the anode off-gas can be successfully oxidized using a spark ignition combustion mode. The fuel conversion efficiency of the anode tail gas is expected to further increase in a more modern engine architecture that can achieve increased burn rates in comparison to the CFR engine. NO x emissions from the combustion of anode off-gas were minimal as the cylinder peak temperatures never exceeded 1800 K. This experimental study ultimately demonstrates the viability of an ICE to operate using an anode off-gas, thus creating a complementary role for an ICE to be paired with a SOFC in a hybrid power generation plant.

Engineering↗
DOE OSTI2018

Investigation of metal sulfide composites as counter electrodes for improved performance of quantum dot sensitized solar cells

Highlights: • The different metal sulfides were synthesized by simple chemical method. • CuS/CoS could increase the V oc value without sacrificing the J sc value. • The electron injection into the electrolyte was enhanced by CuS/CoS CE. • CuS/CoS CE showed the higher power conversion efficiency (5.22%). - Abstract: The electrochemical performance of counter electrodes (CEs) plays an important role for achieving high efficient quantum dot sensitized solar cells (QDSSCs). Considering the optical band gap energy of semiconductor materials and the V{sub oc} of the QDSSCs is determined by the energy difference between the quasi-Fermi levels ({sub q}E{sub f}) of the anode and cathode, so in this work, we synthesized the different metal sulfides and their composites including CuS/CoS, CuS/NiS, CuS, CoS and NiS by chemical bath deposition (CBD) method and used as CEs of QDSSCs. The effect of different CEs on performance of cells were investigated, and the best power conversion efficiency (η) of 5.22% was achieved by CuS/CoS CE, which is higher than that of CuS/NiS, CuS, CoS and NiS (η = 2.56%, 4.73%, 2.23% and 1.62%). The improved cell efficiency was attributed to the excellent electrical conductivity and catalytic activity of CuS and CoS, respectively. The result indicated that the combination of different metal sulfide composites could increase open-circuit voltage (V{sub oc}) value without sacrificing the short-circuit current (J{sub sc}), and leaving good perspectives for significantly higher solar cell performances.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Multi–Resonant Mie Resonator Arrays for Broadband Light Trapping in Ultrathin c–Si Solar Cells

Effective photon management is critical to realize high power conversion efficiencies for thin crystalline silicon (c–Si) solar cells. Standard few–100–µm–thick bulk cells achieve light trapping with macroscopic surface textures covered by thin, continuous antireflection coatings. Such sizeable textures are challenging to implement on ultrathin cells. Here, it is illustrated how nanoscale Mie–resonator–arrays with a bimodal size distribution support multiple resonances that can work in concert to achieve simultaneous antireflection and light–trapping across the broad solar spectrum. The effectiveness of these light–trapping antireflection coatings is experimentally demonstrated on a 2.8 µm–thick c–Si solar cell. The measured short–circuit current and corresponding power conversion efficiency are notably improved, achieving efficiencies as high as 11.2%. Measurements of the saturation current density on completed cells indicate that thermal oxides can effectively limit surface recombination. Finally, the presented design principles are applicable to a wide range of solar cells.

14 SOLAR ENERGY↗
DOE OSTI2021

Quantifying Bulk and Surface Recombination in CdTe Solar Cells Using Time-Resolved Terahertz Spectroscopy

Understanding the nature of recombination mechanisms is essential for higher power conversion efficiency in photovoltaic (PV) devices. Here we use a combination of time-resolved terahertz spectroscopy and numerical modeling to determine the bulk Shockley-Read-Hall lifetime and interface and back surface recombination velocities in CdTe thin film stacks. Furthermore, the measurement was facilitated by fabricating wire-grid device structures using conventional laser scribing. Evaluation of a glass/FTO/SnO2/CdS/CdTe stack treated with CdCl2 allowed separation of the CdTe absorber bulk lifetime, 1.6 ns, from the back surface recombination velocity, ~6x10 4 cm/s, and indicated that CdTe/CdS interface recombination velocity had no significant impact on carrier dynamics.

14 SOLAR ENERGY↗