Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “conversion efficiency”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

In situ Al 2 O 3 incorporation enhances the efficiency of CuIn(S,Se) 2 solar cells prepared from molecular-ink solutions

Here, we report an efficiency enhancement of solution-processed CuIn(S,Se) 2 (CISSe) thin film solar cells via in situ incorporation of Al 2 O 3 . These films were produced using inks containing CuCl, InCl 3 , AlNO 3 (Al/Al + In: 0.1) and thiourea dissolved in methanol. After spin coating of these solutions in air, samples were subjected to a selenization process. Auger electron spectroscopy depth-profiling analysis showed that Al is evenly distributed throughout the bulk of the film. Transmission electron microscopy revealed that AlNO 3 precursor reacted with oxygen to form nanosized amorphous Al 2 O 3 grains located within the bulk and grain boundaries of CISSe, as well as at both the top and bottom interfaces. Power conversion efficiency (PCE) as high as 11.6% (JS C : 35.8 mA cm –2 , V OC : 518 mV, FF: 62.2%, no anti-reflection coating) was achieved with Al–CISSe solar cell devices integrated with CdS (chemical bath deposition, thickness: 80 nm) and ZnO/ITO bilayers (sputtered, thickness: 300 nm). The average PCE (10.1%, $\langle$J SC $\rangle$: 34.5 mA cm –2 , $\langle$V OC $\rangle$: 491 mV, $\langle$FF$\rangle$: 59.8%) was nearly 4% (absolute) higher than that measured on CISSe baseline cells fabricated from solutions without Al ($\langle$PCE$\rangle$ = 6.4%, $\langle$J SC $\rangle$: 32.8 mA cm –2 , $\langle$V OC $\rangle$: 410 mV, $\langle$FF$\rangle$: 47.3%). This in situ Al 2 O 3 incorporation is speculated to play a role in the enhancement of the VOC and FF of the devices through passivation of defects in CISSe reducing interface and bulk recombination, as evidenced by a reduced defect density and an increased activation energy of the dominant recombination mechanism from capacitance and temperature-dependent VOC measurements, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Efficiency and cost advantages of an advanced-technology nuclear electrolytic hydrogen-energy production facility

The concept of an advanced-technology (viz., 1985 technology) nuclear-electrolytic water electrolysis facility was assessed for hydrogen production cost and efficiency expectations. The facility integrates (1) a high-temperature gas-cooled nuclear reactor (HTGR) operating a binary work cycle, (2) direct-current (d-c) electricity generation via acyclic generators, and (3) high-current-density, high-pressure electrolyzers using a solid polymer electrolyte (SPE). All subsystems are close-coupled and optimally interfaced for hydrogen production alone (i.e., without separate production of electrical power). Pipeline-pressure hydrogen and oxygen are produced at 6900 kPa (1000 psi). We found that this advanced facility would produce hydrogen at costs that were approximately half those associated with contemporary-technology nuclear electrolysis: $5.36 versus $10.86/million Btu, respectively. The nuclear-heat-to-hydrogen-energy conversion efficiency for the advanced system was estimated as 43%, versus 25% for the contemporary system.

Donakowski, T. D.↗
DOE OSTI2022

Hot-Casting-Assisted Liquid Additive Engineering for Efficient and Stable Perovskite Solar Cells

High-performance inorganic–organic lead halide perovskite solar cells (PSCs) are often fabricated with a liquid additive such as dimethyl sulfoxide (DMSO), which retards crystallization and reduces roughness and pinholes in the perovskite layers. However, DMSO can be trapped during perovskite film formation and induce voids and undesired reaction byproducts upon later processing steps. Here, it is shown that the amount of residual DMSO can be reduced in as-spin-coated films significantly through use of preheated substrates, or a so-called hot-casting method. Hot casting increases the perovskite film thickness given the same concentration of solutions, which allows for reducing the perovskite solution concentration. By reducing the amount of DMSO in proportion to the concentration of perovskite precursors and using hot casting, it is possible to fabricate perovskite layers with improved perovskite–substrate interfaces by suppressing the formation of byproducts, which increase trap density and accelerate degradation of the perovskite layers. The best-performing PSCs exhibit a power conversion efficiency (PCE) of 23.4% (23.0% stabilized efficiency) under simulated solar illumination. Furthermore, encapsulated devices show considerably reduced post-burn-in decay, retaining 75% and 90% of their initial and post-burn-in efficiencies after 3000 h of operation with maximum power point tracking (MPPT) under high power of ultraviolet (UV)-containing continuous light exposure.

perovskite-substrate interface↗
DOE OSTI2021

Polymer Hole Transport Materials for Perovskite Solar Cells via Buchwald–Hartwig Amination

The development of low-cost materials for charge-selective contacts that provide good energetic alignment with perovskite active layers, favorable thermal properties, and lead to efficient photoconversion is becoming an increasingly important aspect of the perovskite solar cell (PSC) field. Presented here is a series of polymers based on a one-pot polymerization of aryl dihalides with primary aryl amines to produce solution-processable polymers in high yield, with simple purification, and promising properties for high performing P-I-N PSC devices. How these properties can be tuned by careful selection of the reactant chemical moieties is discussed. Through this strategy, a wide range of relevant properties such as glass transition temperature, highest occupied molecular orbital tuning, and polydispersity are explored. When implemented into devices using a triple-cation FAMACs perovskite active layer, the hole transport material series shows average power conversion efficiencies (PCE) in excess of 17%, which is comparable to controls using state-of-the-art poly(triarylamine). How different synthetic parameters such as the reaction time and purification protocol impact device performance is also investigated.

14 SOLAR ENERGY↗
NASA NTRS1992

Progress on single barrier varactors for submillimeter wave power generation

Theoretical work on Single Barrier Varactor (SBV) diodes, indicate that the efficiency for a multiplier has a maximum for a considerably smaller capacitance variation than previously thought. The theoretical calculations are performed, both with a simple theoretical model and a complete computer simulation using the method of harmonic balance. Modeling of the SBV is carried out in two steps. First, the semiconductor transport equations are solved simultaneously using a finite difference scheme in one dimension. Secondly, the calculated I-V, and C-V characteristics are input to a multiplier simulator which calculates the optimum impedances, and output powers at the frequencies of interest. Multiple barrier varactors can also be modeled in this way. Several examples on how to design the semiconductor layers to obtain certain characteristics are given. The calculated conversion efficiencies of the modeled structures, in a multiplier circuit, are also presented. Computer simulations for a case study of a 750 GHz multiplier show that InAs diodes perform favorably compared to GaAs diodes. InAs and InGaAs SBV diodes have been fabricated and their current vs. voltage characteristics are presented. In the InAs diode, was the large bandgap semiconductor AlSb used as barrier. The InGaAs diode was grown lattice matched to an InP substrate with InAlAs as a barrier material. The current density is greatly reduced for these two material combinations, compared to that of GaAs/AlGaAs SBV diodes. GaAs based diodes can be biased to higher voltages than InAs diodes.

Nilsen, Svein M.↗
DOE OSTI2022

III-V Solar Cells with Novel Epitaxial Lift-off Architectures for Extended Substrate Reuse for Low-cost Manufacturing

The highest solar cell efficiencies have been achieved with III-V photovoltaics (PV). Still, the use of III-V materials in terrestrial applications has been very limited, mainly because of their high cost. The high cost is primarily due to the expensive Ge or GaAs wafers which could amount up to one-half of the total module cost! A prominent approach to reduce the impact of the high cost of substrates used for III-V PV is through re-use of the wafer substrates by Epitaxial Lift-Off (ELO). Typically, using a sacrificial layer such as AlAs, the device part of the cell is lifted off, leaving behind the substrate for re-use for fabrication of the next device. While conversion efficiency as high as 29.1% has been achieved by ELO method, chemical mechanical polishing (CMP) of the substrate is required which significantly adds to the overall solar cell cost. In this project, we have developed a novel ELO architecture for single junction gallium arsenide (GaAs) solar cells that will not require CMP of the substrate for re-use. Multiple reuses of GaAs wafers have been demonstrated with no CMP, without degradation in solar cell efficiency. Also, the solar cells have been successfully lifted off and transferred to inexpensive substrates with less than 2% change in efficiency. By elimination of the CMP process, which is the highest cost component of III-V solar cells made by conventional ELO method (~$10/W), and decreasing the substrate cost by multiple re-uses, the developed technology could be a leap forward in significantly reducing the cost of III-V photovoltaics.

14 SOLAR ENERGY↗
NASA NTRS2007

Thermoelectric Energy Conversion: Future Directions and Technology Development Needs

This viewgraph presentation reviews the process of thermoelectric energy conversion along with key technology needs and challenges. The topics include: 1) The Case for Thermoelectrics; 2) Advances in Thermoelectrics: Investment Needed; 3) Current U.S. Investment (FY07); 4) Increasing Thermoelectric Materials Conversion Efficiency Key Science Needs and Challenges; 5) Developing Advanced TE Components & Systems Key Technology Needs and Challenges; 6) Thermoelectrics; 7) 200W Class Lightweight Portable Thermoelectric Generator; 8) Hybrid Absorption Cooling/TE Power Cogeneration System; 9) Major Opportunities in Energy Industry; 10) Automobile Waste Heat Recovery; 11) Thermoelectrics at JPL; 12) Recent Advances at JPL in Thermoelectric Converter Component Technologies; 13) Thermoelectrics Background on Power Generation and Cooling Operational Modes; 14) Thermoelectric Power Generation; and 15) Thermoelectric Cooling.

theromelectric↗
DOE OSTI2023

Benzo[d]thiazole Based Wide Bandgap Donor Polymers Enable 19.54% Efficiency Organic Solar Cells Along with Desirable Batch-to-Batch Reproducibility and General Applicability

The limited selection pool of high-performance wide bandgap (WBG) polymer donors is a bottleneck problem of the nonfullerene acceptor (NFA) based organic solar cells (OSCs) that impedes the further improvement of their photovoltaic performances. In this work, a series of new WBG polymers, namely PH-BTz, PS-BTz, PF-BTz, and PCl-BTz, are developed by using the bicyclic difluoro-benzo[d]thiazole (BTz) as the acceptor block and benzo[1,2-b:4,5-b']dithiophene (BDT) derivatives as the donor units. By introducing S, F, and Cl atoms to the alkylthienyl sidechains on BDT, the resulting polymers exhibit lowered energy levels and enhanced aggregation properties. The fluorinated PBTz-F not only exhibits a low-lying HOMO level, but also has stronger face-on packing order and results in more uniform fibril-like interpenetrating networks in the related PF-BTz:L8-BO blend. A high-power conversion efficiency (PCE) of 18.57% is achieved. Moreover, PBTz-F also exhibits a good batch-to-batch reproducibility and general applicability. In addition, ternary blend OSCs based on the host PBTz-F:L8-BO blend and PM6 guest donor exhibits a further enhanced PCE of 19.54%, which is among the highest values of OSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Synergy of Liquid-Crystalline Small-Molecule and Polymeric Donors Delivers Uncommon Morphology Evolution and 16.6% Efficiency Organic Photovoltaics

Achieving an ideal morphology is an imperative avenue for enhancing key parameters toward high-performing organic solar cells (OSCs). Among a myriad of morphological-control methods, the strategy of incorporating a third component with structural similarity and crystallinity difference to construct ternary OSCs has emerged as an effective approach to regulate morphology. A nematic liquid-crystalline benzodithiophene terthiophene rhodamine (BTR) molecule, which possesses the same alkylthio-thienyl-substituted benzo moiety but obviously stronger crystallinity compared to classical medium-bandgap polymeric donor PM6, is employed as a third component to construct ternary OSCs based on a PM6:BTR:Y6 system. The doping of BTR (5 wt%) is found to be enough to improve the OSC morphology—significantly enhancing the crystallinity of the photoactive layer while slightly reducing the donor/acceptor phase separation scale simultaneously. Rarely is such a morphology evolution reported. It positively affects the electronic properties of the device—prolongs the carrier lifetime, shortens the photocurrent decay time, facilitates exciton dissociation, charge transport, and collection, and ultimately boosts the power conversion efficiency from 15.7% to 16.6%. This result demonstrates that the successful synergy of liquid-crystalline small-molecule and polymeric donors delicately adjusts the active-layer morphology and refines device performance, which brings vibrancy to the OSC research field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

N-dopants optimize the utilization of spontaneously formed photocharges in organic solar cells

Non-fullerene acceptors (NFAs) not only bring rapid efficiency progress to organic solar cells (OSCs) but have also generated scientific interest in re-evaluating the photocharge generation route via spontaneous or heterojunction-assisted charge separation. In this work, we propose the addition of n-dopants as a strategy to optimize the utilization of spontaneously formed photocharges in NFAs and construct ultralow donor-content dilute bulk heterojunction (BHJ) devices to validate the dopant's roles. N-dopants enhance the transport length of spontaneously formed photocharges over twofold and alleviate the bimolecular recombination with balanced carrier mobility during charge extraction. This improves the photocurrent of ultralow donor-content dilute BHJ devices by over 2.4 times. Moreover, these benefits are successfully conducted to the BHJ devices, and enhancement of conversion efficiencies is observed in both the 100 nm and 400 nm thick OSCs. Our results provide a feasible way to optimize the intrinsic photocharges in NFAs and renew the possibility of efficient single-component OSCs as inorganic photovoltaic techniques.

14 SOLAR ENERGY↗
NASA NTRS1988

The global Cretaceous-Tertiary fire: Biomass or fossil carbon

The global soot layer at the K-T boundary indicates a major fire triggered by meteorite impact. However, it is not clear whether the principal fuel was biomass or fossil carbon. Forests are favored by delta value of C-13, which is close to the average for trees, but the total amount of elemental C is approximately 10 percent of the present living carbon, and thus requires very efficient conversion to soot. The PAH was analyzed at Woodside Creek, in the hope of finding a diagnostic molecular marker. A promising candidate is 1-methyl-7-isopropyl phenanthrene (retene,), which is probably derived by low temperature degradation of abietic acid. Unlike other PAH that form by pyrosynthesis at higher temperatures, retene has retained the characteristic side chains of its parent molecule. A total of 11 PAH compounds were identified in the boundary clay. Retene is present in substantial abundance. The identification was confirmed by analysis of a retene standard. Retene is characteristic of the combustion of resinous higher plants. Its formation depends on both temperature and oxygen access, and is apparently highest in oxygen-poor fires. Such fires would also produce soot more efficiently which may explain the high soot abundance. The relatively high level of coronene is not typical of a wood combustion source, however, though it can be produced during high temperature pyrolysis of methane, and presumably other H, C-containing materials. This would require large, hot, low O2 zones, which may occur only in very large fires. The presence of retene indicates that biomass was a significant fuel source for the soot at the Cretaceous-Tertiary boundary. The total amount of elemental C produced requires a greater than 3 percent soot yield, which is higher than typically observed for wildfires. However, retene and presumably coronene imply limited access of O2 and hence high soot yield.

Gilmour, Iain↗
DOE OSTI2024

Improving Miscibility of Polymer Donor and Polymer Acceptor by Reducing Chain Entanglement for Realizing 18.64 % Efficiency All Polymer Solar Cells

All-polymer solar cells have experienced rapid development in recent years by the emergence of polymerized small molecular acceptors (PSMAs). However, the strong chain entanglements of polymer donors (P D s) and polymer acceptors (P A s) decrease the miscibility of the resulting polymer mixtures, making it challenging to optimize the blend morphology. Herein, we designed three P A s, namely PBTPICm-BDD, PBTPICγ-BDD and PBTPICF-BDD, by smartly using a BDD unit as the polymerized unit to copolymerize with different Y-typed non-fullerene small molecular acceptors (NF-SMAs), thus achieving a certain degree of distortion and giving the polymer system enough internal space to reduce the entanglements of the polymer chains. Such effects increase the chances of the P D being interspersed into the acceptor material, which improve the solubility between the P D and P A . The PBTPICγ-BDD and PBTPICF-BDD displayed better miscibility with PBQx-TCl, leading to a well optimized morphology. As a result, high power conversion efficiencies (PCEs) of 17.50 % and 17.17 % were achieved for PBQx-TCl : PBTPICγ-BDD and PBQx-TCl : PBTPICF-BDD devices, respectively. In conclusion, with the addition of PYFT-o as the third component into PBQx-TCl : PBTPICγ-BDD blend to further extend the absorption spectral coverage and finely tune microstructures of the blend morphology, a remarkable PCE of 18.64 % was realized finally.

36 MATERIALS SCIENCE↗
DOE OSTI2023

19.32% Efficiency Polymer Solar Cells Enabled by Fine-Tuning Stacking Modes of Y-Type Molecule Acceptors: Synergistic Bromine and Fluorine Substitution of the End Groups

Here, the success of Y6-type nonfullerene small molecule acceptors (NF-SMAs) in polymer solar cells (PSCs) can be attributed to their unique honeycomb stacking style, which leads to favorable thin-film morphologies. The intermolecular interactions related to the crystallization tendency of these NF-SMAs is closely governed by their electron accepting end groups. For example, the high performance Y6 derivative L8-BO (BTP-4F) presents three types of stacking modes in contrast to two stacking modes of Y6. Hence, it is ultimately interesting to obtain more insight on the packing properties and the preferences influenced by chemical modifications such as end group engineering. This work designs and synthesizes asymmetric and symmetric L8-BO derivatives with brominated end groups and explores the stacking preferences in various modes. The asymmetric BTP-3FBr displays an optimized crystallization tendency and thin film morphology, leading to a decent power conversion efficiency (PCE) of 18.34% in binary devices and a top PCE of 19.32% in ternary devices containing 15 wt% IDIC as the second acceptor.

36 MATERIALS SCIENCE↗
NASA NTRS2001

Novel High Efficient Organic Photovoltaic Materials

In man's mission to the outer space or a remote site, the most abundant, renewable, nonpolluting, and unlimited external energy source is light. Photovoltaic (PV) materials can convert light into electrical power. In order to generate appreciable electrical power in space or on the Earth, it is necessary to collect sunlight from large areas due to the low density of sunlight, and this would be very costly using current commercially available inorganic solar cells. Future organic or polymer based solar cells seemed very attractive due to several reasons. These include lightweight, flexible shape, ultra-fast optoelectronic response time (this also makes organic PV materials attractive for developing ultra-fast photo detectors), tunability of energy band-gaps via molecular design, versatile materials synthesis and device fabrication schemes, and much lower cost on large-scale industrial production. It has been predicted that nano-phase separated block copolymer systems containing electron rich donor blocks and electron deficient acceptor blocks will facilitate the charge separation and migration due to improved electronic ultrastructure and morphology in comparison to current polymer composite photovoltaic system. This presentation will describe our recent progress in the design, synthesis and characterization of a novel donor-bridge-acceptor block copolymer system for potential high-efficient organic optoelectronic applications. Specifically, the donor block contains an electron donating alkyloxy derivatized polyphenylenevinylene, the acceptor block contains an electron withdrawing alkyl-sulfone derivatized polyphenylenevinylene, and the bridge block contains an electronically neutral non-conjugated aliphatic hydrocarbon chain. The key synthetic strategy includes the synthesis of each individual block first, then couple the blocks together. While the donor block stabilizes the holes, the acceptor block stabilizes the electrons. The bridge block is designed to hinder the electron-hole recombination. Thus, improved charge separation is expected. In addition, charge migration will also be facilitated due to the expected nano-phase separated and highly ordered block copolymer ultrastructural. The combination of all these factors will result in significant overall enhancement of photovoltaic power conversion efficiency.

Sun, Sam↗
DOE OSTI2024

High‐Performance Ternary Organic Solar Cells with Enhanced Luminescence Efficiency and Miscibility Enabled by Two Compatible Acceptors

Abstract The ternary strategy has proven to be an effective method for improving the efficiency of organic solar cells (OSCs). However, designing and selecting the third component still pose challenges. In this study, this issue is addressed by focusing on the PBDB‐T:Y18‐F binary system and introducing a new, strong luminescent, asymmetric small‐molecule acceptor (SMA) called L8‐CBIC‐Cl, which shares a similar skeleton with Y18‐F. The similarity in molecular framework facilitates good compatibility between the two acceptors, resulting in the formation of an alloy‐like acceptor phase. Furthermore, the norbornenyl‐modified end group in L8‐CBIC‐Cl contributes to its strong luminescent properties, which in turn leads to a low non‐radiative energy loss and a high open‐circuit voltage. Consequently, the PBDB‐T:L8‐CBIC‐Cl:Y18‐F based ternary devices realize a high power conversion efficiency (PCE) up to 17.01%, which is higher than PBDB‐T:Y18‐F device (14.49%). Importantly, L8‐CBIC‐Cl exhibits a good universality as a guest acceptor in other three binary systems (D18:Y6, D18:BTP‐eC9‐4F, and D18:L8‐BO). The D18:L8‐BO:L8‐CBIC‐Cl device shows an impressive efficiency of 19%. The work demonstrates that employing SMA with a high PLQY and better miscibility with host acceptor as the third component has a great potential for developing high‐efficiency ternary OSCs.

Chemistry↗
DOE OSTI2022

Pseudo-halide anion engineering for efficient quasi-2D Ruddlesden-Popper tin perovskite solar cells

Quasi-two-dimensional (2D) organic-inorganic hybrid tin perovskites have emerged as promising alternatives to lead-based perovskites in thin-film photovoltaics because of their reduced toxicity and improved stability. However, the undesired small n-value 2D phases and disordered crystal orientation enormously restrict the efficiency of quasi-2D tin perovskite solar cells (PSCs) due to uncontrollable nucleation and crystal growth processes. Here, we propose a mixed pseudo-halide anion engineering approach by using acetate (Ac - ) and tetrafluoroborate (BF 4 - ) anions to make quasi-2D Ruddlesden-Popper perovskites with a target formula of PEA 2 FA 4 Sn 5 I 16 . We find that the mixed Ac - and BF 4 - anions can not only promote homogeneously distributed PEA + cations in the precursor by effectively breaking the PEA + ···PEA + stacking but also retard the crystallization process by coordinating with unbonded SnI 2 , thereby, significantly reducing small n-value 2D phases, improving the crystal orientation, and suppressing the Sn 2+ oxidation. The resulting PSC exhibits up to 9% power conversion efficiency and 400 h stability.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Compositional texture engineering for highly stable wide-bandgap perovskite solar cells

The development of highly stable and efficient wide-bandgap (WBG) perovskite solar cells (PSCs) based on bromine-iodine (Br–I) mixed-halide perovskite (with Br greater than 20%) is critical to create tandem solar cells. However, issues with Br–I phase segregation under solar cell operational conditions (such as light and heat) limit the device voltage and operational stability. This challenge is often exacerbated by the ready defect formation associated with the rapid crystallization of Br-rich perovskite chemistry with antisolvent processes. We combined the rapid Br crystallization with a gentle gas-quench method to prepare highly textured columnar 1.75–electron volt Br–I mixed WBG perovskite films with reduced defect density. Here, with this approach, we obtained 1.75–electron volt WBG PSCs with greater than 20% power conversion efficiency, approximately 1.33-volt open-circuit voltage (V oc ), and excellent operational stability (less than 5% degradation over 1100 hours of operation under 1.2 sun at 65°C). When further integrated with 1.25–electron volt narrow-bandgap PSC, we obtained a 27.1% efficient, all-perovskite, two-terminal tandem device with a high V oc of 2.2 volts.

14 SOLAR ENERGY↗