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At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
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↗
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↗
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↗
DOE OSTI2023

Developing Efficient Benzene Additives for 19.43% Efficiency of Organic Solar Cells by Crossbreeding Effect of Fluorination and Bromination

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. In this work, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5-trifluorobenzene, hexafluorobenzene, 1,3,5-tribromo-2,4,6-trifluorobenzene (TFTB), 1,3,5-tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz-F:PM6:L8-BO system.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Modulation of End Groups for Low‐Bandgap Nonfullerene Acceptors Enabling High‐Performance Organic Solar Cells

Abstract The field of nonfullerene organic solar cells (OSCs) has seen an impressive progress, largely due to advances in high‐performance small molecule acceptors (SMAs). As a large portion of the solar energy is located in the near‐infrared region, it is important to develop ultralow‐bandgap SMAs that have extended absorption in the spectral range of 800–1000 nm to maximize light absorption and efficiencies. In this work, three low‐bandgap SMAs, namely, IXIC, IXIC‐2Cl, and IXIC‐4Cl, are designed and synthesized with same fused terthieno[3,2‐ b ]thiophene donor unit and different end groups (EGs). The three SMAs all have low optical bandgap ( E g ) of 1.35, 1.30, and 1.25 eV, respectively. The chlorination on EGs can lower the energy level and broaden absorption range of the SMAs. As a result, the V oc of the devices is reduced but the J sc is significantly increased. In addition, the addition of chlorine atoms can enhance π–π stacking and crystallinity of the SMAs, which result in high fill factors. Overall, the optimum EGs are monochlorine‐substituted IC and OSCs based on PBDB‐T:IXIC‐2Cl that can achieve remarkable power conversion efficiencies (PCEs) of 12.2%, which is one of the highest PCEs for nonfullerene organic solar cells based on low‐bandgap SMAs.

Chen, Yuzhong↗
DOE OSTI2017

Effect of Alkylsilyl Side‐Chain Structure on Photovoltaic Properties of Conjugated Polymer Donors

Abstract Side‐chain engineering is an important strategy for optimizing photovoltaic properties of organic photovoltaic materials. In this work, the effect of alkylsilyl side‐chain structure on the photovoltaic properties of medium bandgap conjugated polymer donors is studied by synthesizing four new polymers J70 , J72 , J73 , and J74 on the basis of highly efficient polymer donor J71 by changing alkyl substituents of the alkylsilyl side chains of the polymers. And the photovoltaic properties of the five polymers are studied by fabricating polymer solar cells (PSCs) with the polymers as donor and an n‐type organic semiconductor (n‐OS) m ‐ITIC as acceptor. It is found that the shorter and linear alkylsilyl side chain could afford ordered molecular packing, stronger absorption coefficient, higher charge carrier mobility, thus results in higher J sc and fill factor values in the corresponding PSCs. While the polymers with longer or branched alkyl substituents in the trialkylsilyl group show lower‐lying highest occupied molecular orbital energy levels which leads to higher V oc of the PSCs. The PSCs based on J70 : m ‐ITIC and J71 : m ‐ITIC achieve power conversion efficiency (PCE) of 11.62 and 12.05%, respectively, which are among the top values of the PSCs reported in the literatures so far.

Bin, Haijun↗
DOE OSTI2018

The role of oxygen doping on elemental intermixing at the PVD-CdS/Cu (InGa)Se 2 heterojunction

Elemental intermixing at the CdS/CuIn 1-x Ga x Se 2 (CIGS) heterojunction in thin-film photovoltaic devices plays a crucial role in carrier separation and thus device efficiency. Here, using scanning transmission electron microcopy in combination with energy dispersive X-ray mapping, we find that by controlling the oxygen in the sputtering gas during physical vapor deposition (PVD) of the CdS, we can tailor the degree of elemental intermixing. More oxygen suppresses Cu migration from the CIGS into the CdS, while facilitating Zn doping in the CdS from the ZnO transparent contact. Very high oxygen levels induce nanocrystallinity in the CdS, while moderate or no oxygen content can promote complete CdS epitaxy on the CIGS grains. Regions of cubic Cu 2 S phase were observed in the Cu-rich CdCuS when no oxygen is included in the CdS deposition process. In the process-of-record sample (moderate O 2 ) that exhibits the highest solar conversion efficiency, we observe a ~26-nm-thick Cu-deficient CIGS surface counter-doped with the highest Cd concentration among all of the samples. Cd movement into the CIGS was found to be less than 10 nm deep for samples with either high or zero O 2 . Lastly, the results are consistent with the expectation that Cd doping of the CIGS surface and lack of Zn diffusion into the buffer both enhance device performance.

14 SOLAR ENERGY↗
DOE OSTI2014

Facile method for synthesis of TiO{sub 2} film and its application in high efficiency dye sensitized-solar cell (DSSC)

Dye-sensitized solar cells (DSSC) is a device which converts a solar energy to electrical energy. Different with semiconductor thin film based solar cell, DSSC utilize the sensitized-dye to absorb the photon and semiconductor such as titanium dioxide (TiO{sub 2}) and zinc oxide (ZnO) as a working electrode photoanode. In this report, the preparation of TiO{sub 2} film using a facile method of spray deposition and its application in DSSC have been presented. TiO{sub 2} photoanode was synthesized by growing the droplet of titanium tetraisopropoxide diluted in acid solution on the substrate of conductive glass flourine-doped tin oxide (FTO) with variation of precursor volume. DSSC was assemblied by sandwiching both of photoanode electrode and platinum counter electrode subsequently filling the area between these electrodes with triodine/iodine electrolite solution as redox pairs. The characterization of the as prepared DSSC using solar simulator (AM 1.5G, 100 mW/cm{sup 2}) and I-V source meter Keithley 2400 showed that the performance of DSSC was affected by the precursor volume.. The overall conversion efficiency of DSSC using the optimum TiO{sub 2} film was about 1.97% with the open circuit voltage (V{sub oc}) of 0.73 V, short circuit current density (J{sub sc}) of 4.61 mA and fill factor (FF) of 0.58.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Templated Growth and Passivation of Vertically Oriented Antimony Selenide Thin Films for High-Efficiency Solar Cells in Substrate Configuration

Antimony selenide (Sb 2 Se 3 ) is a promising low-cost photovoltaic material with a 1D crystal structure. The grain orientation and defect passivation play a critical role in determining the performance of polycrystalline Sb 2 Se 3 thin-film solar cells. In this work, a seed layer is introduced on a molybdenum (Mo) substrate to template the growth of a vertically oriented, columnar Sb 2 Se 3 absorber layer by closed space sublimation. By controlling the grain orientation and compactness of the Sb 2 Se 3 seeds, obtain high-quality Sb 2 Se 3 absorber layers with passive Sb 2 Se 3 /Mo interfaces is obtained, which in turn improve the transport of photoexcited charge carriers through the absorber layer and its interfaces. Post-deposition annealing of absorber layers in ambient air is further utilized to passivate the defects in Sb 2 Se 3 and enhance the quality of the front heterojunction. As a result of systematic processing optimization, Sb 2 Se 3 planar heterojunction solar cells are fabricated in substrate configuration with a champion power conversion efficiency of 8.5%.

14 SOLAR ENERGY↗
DOE OSTI2024

Iodine Modulates the MACl‐Assisted Growth of FAPbI 3 for High Efficiency Perovskite Solar Cells

The preferential growth of α-phase formamidinium perovskite (α-FAPbI 3 ) at low temperatures can be achieved with the incorporation of chloride-based additives, with methylammonium chloride (MACl) being the most common example. However, compared to other less-volatile chloride additives, MACl only remains in the growing perovskite film for a short time before evaporating during annealing, primarily influencing the early stages of film formation. In addition, evaporation of MACl as methylamine (MA 0 ) and HCl can introduce a side reaction between MA 0 and formamidinium (FA), undermining the compositional purity and phase stability of α-FAPbI 3 . In this study, it is demonstrated that addition of iodine (I 2 ) into the FAPbI 3 precursor solution containing MACl suppresses the MA-FA side reaction during annealing. Additionally, MACl evaporation is delayed owing to strong interaction with triiodide. The added I 2 facilitates spontaneous growth of α-FAPbI 3 prior to annealing, with an improved bottom morphology due to the formation of fewer byproducts. Perovskite solar cells derived from an I 2 -incorporated solution deliver a champion power conversion efficiency of 25.2% that is attributed to suppressed non-radiative recombination.

14 SOLAR ENERGY↗
DOE OSTI2016

Optical-Vibrational Properties of the Cs 2 SnX 6 (X = Cl, Br, I) Defect Perovskites and Hole-Transport Efficiency in Dye-Sensitized Solar Cells

We report the vibrational and optical properties of the ‘defect’ perovskites Cs 2 SnX 6 (X = Cl, Br, I) as well as their use as hole-transporting materials (HTMs) in solar cells. All three air-stable compounds were characterized using powder X-ray diffraction and Rietveld refinement. Far-IR reflectance, Raman, and UV–vis spectroscopy as well as electronic band structure calculations show that the compounds are direct band gap semiconductors with a pronounced effect of the halogen atom on the size of the energy gap and the vibrational frequencies. Scanning electron microscopy and atomic force microscopy confirmed that the morphology of the perovskite films deposited from $N,N$-dimethylformamide solutions on TiO 2 substrates also strongly depends on the chemical composition of the materials. The Cs 2 SnX 6 perovskites were introduced as hole-transporting materials in dye-sensitized solar cells, based on mesoporous titania electrodes sensitized with various organic and metal–organic dyes. The solar cells based on Cs 2 SnI 6 HTM and the Z907 dye performed best with a maximum power conversion efficiency of 4.23% at 1 sun illumination. The higher performance of Cs 2 SnI 6 is attributed to efficient charge transport in the bulk material and hole extraction at the perovskite-Pt interface, as evidenced by electrochemical impedance spectroscopy.

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

Modulation of PEDOT:PSS pH for efficient inverted perovskite solar cells with reduced potential loss and enhanced stability

Inverted p-i-n perovskite solar cells (PVSCs) using PEDOT:PSS as the hole-transporting layer (HTL) is one of the most widely adopted device structures thus far due to its facile processability and good compatibility for high throughput manufacturing processes. However, most of the PEDOT:PSS-based CH 3 NH 3 PbI 3 PVSCs reported to date suffered an inferior open-circuit voltage (V OC ) (0.88-0.95 V) compared to that (1.05-1.12 V) obtained for common CH 3 NH 3 PbI 3 PVSCs, revealing a severe potential loss issue. Herein, we describe a simple method to alleviate this problem by tuning the pH value of PEDOT:PSS with a mild base, imidazole. Accompanied by the pH modulation, the blended imidazole concurrently tailors the surface texture and electronic properties of PEDOT:PSS to promote the quality and crystallization of the perovskite film deposited on top of it and enable better energy-level alignment at this corresponding interface. Consequently, the PVSC using this modified PEDOT:PSS HTL yields an enhanced power conversion efficiency (PCE) of 15.7% with an enlarged V OC of 1.06 V and improved long-term stability. Lastly, these outperform the pristine device showing a PCE of 12.7% with a much smaller V OC of 0.88 V and unsatisfactory environmental stability.

14 SOLAR ENERGY↗
DOE OSTI2012

Nanosolar: Delivering Grid-Parity Solar Electricity

Nanosolar has developed proprietary technology based on Copper-Indium-Gallium-diSelenide (CIGS) absorber technology that allows the printing of this semiconductor material using a high-speed, high-throughput roll-to-roll manufacturing process. A central challenge in cost-effectively constructing a large-area CIGS-based solar cell or module is that the elements of the CIGS layer must be within a narrow stoichiometric ratio on nano-, meso-, and macroscopic length scale in all three dimensions in order for the resulting cell or module to be highly efficient. Achieving precise stoichiometric composition over relatively large substrate areas is however difficult using traditional vacuum-based deposition processes. For example, it is difficult to uniformly deposit compounds and/or alloys containing more than one element by sputtering or evaporation. Both techniques rely on deposition approaches that are limited to line-of-sight and limited-area sources, tending to result in poor surface coverage. Line-of-sight trajectories and limited-area sources can result in non-uniform three-dimensional distribution of the elements in all three dimensions and/or poor film-thickness uniformity over large areas. These non-uniformities can occur over the nano-, meso-, and/or macroscopic scales. Such non-uniformity also alters the local stoichiometric ratios of the absorber layer, decreasing the potential power conversion efficiency of the complete cell or module. Nanosolar has overcome these challenges by printing nanoparticulate CIGS precursor materials onto low-cost metal foil substrates, and performing a rapid thermal processing to convert the nanoparticulate coating into a CIGS absorber layer By locking in the appropriate stochiometry into the nanoparticulate precursor material, spatial uniformity is ensured in the coated layers, while printing at high speed and throughput minimizes solar cell cost.

14 SOLAR ENERGY↗
DOE OSTI2023

High-Efficiency Modular SiC-based Power-Converter for Flexible-CHP Systems with Stability-Enhanced Grid-Support Functions

This project seeks to develop a modular, scalable MV power converter featuring stability-enhanced grid-support functions for future grid-interface applications in flexible combined heat and power (F-CHP) cogeneration plants, being fully compliant with the IEEE Standard 1547, category B—for operation in local areas with high aggregated distributed energy resource (DER) penetration, and also with the IEEE standard for the specification of microgrid controllers, namely IEEE Std 2030.7, with the goal to enable F-CHP systems for both microgrid and standalone applications. Further, the proposed converter will use a modular circuit topology, the MMC, which is scalable both in voltage and current by interconnecting power-cell building blocks, thus flexibly suiting the needs of F-CHP systems in the 1–20 MWe range. Furthermore, the use of 10 kV SiC MOSFET devices will minimize the number of power-cells needed to operate in 2–13.8 kV MV distribution systems, but more importantly, they will render feasible a power conversion efficiency > 98 %, and a power density > 10 kW/l. This is highly relevant given that these are two key performance metrics that will further increase the value of F-CHP systems by shortening the time required to recover their investment costs.

14 SOLAR ENERGY↗
DOE OSTI2013

Dominant deuteron acceleration with a high-intensity laser for isotope production and neutron generation

Experiments on the interaction of an ultra-short pulse laser with heavy-water, ice-covered copper targets, at an intensity of 2 Multiplication-Sign 10{sup 19} W/cm{sup 2}, were performed demonstrating the generation of a 'pure' deuteron beam with a divergence of 20 Degree-Sign , maximum energy of 8 MeV, and a total of 3 Multiplication-Sign 10{sup 11} deuterons with energy above 1 MeV-equivalent to a conversion efficiency of 1.5%{+-} 0.2%. Subsequent experiments on irradiation of a {sup 10}B sample with deuterons and neutron generation from d-d reactions in a pitcher-catcher geometry, resulted in the production of {approx}10{sup 6} atoms of the positron emitter {sup 11}C and a neutron flux of (4{+-}1) Multiplication-Sign 10{sup 5} neutrons/sterad, respectively.

43 PARTICLE ACCELERATORS↗