Electron Donor Component Research Articles

Homocoupling defects in porphyrinoid small molecules and their effect on organic solar cell performance

Abstract Porphyrinoid small molecules can be used as electron donor or acceptor components in bulk heterojunction organic solar cells, which has resulted in steadily improving power conversion efficiencies. However, the effect of material purity is often neglected. In this work, a series of D1-A-π-D2-π-A-D1 conjugated chromophores based on the A2B2-meso-ethynylporphyrin core is synthesized. Different electron-donating (D1) end groups are chosen to investigate their influence on the material properties and optoelectronic characteristics. The porphyrin small molecules are tested as electron donor materials in bulk heterojunction organic solar cells in combination with PC71BM, affording an efficiency up to 4.6% under standard illumination. Furthermore, it is shown that (Glaser type) homocoupled side products are generated during the final Sonogashira cross-coupling reactions, which can be very challenging to remove. Their presence reduces solar cell performance by affecting the open-circuit voltage and fill factor.

Mitigation of Soot Deposition on Modified Surfaces of Exhaust Gas Recirculation Coolers

A common approach for lower emission of NOx from diesel engines is to use exhaust gas recirculation (EGR) coolers where part of the exhaust gas is returned to the cylinder to reduce the combustion temperature. Nonetheless, the deposition of various species, i.e. soot particles, on surfaces deteriorates the thermal efficiency of EGR coolers. This study investigated the impact of surface treatment on particulate fouling of a rectangular EGR cooler. An experimental setup was assembled through which the uncoated and coated plates were exposed to the flow of exhaust flue gases. The cooler surfaces were coated by ceramic-based materials with resistance to high temperatures by spraying. The results showed that surface modification abated soot deposition to some extent and the deposit layer was easily flaked off with a force of 0.8 N when it was scratched with a nano-intender. Contrariwise, the deposit formed on the uncoated surface did not result in similar propensity and instead it required a larger force of 2.25 N. This implies weaker stickiness of soot deposit on the investigated coatings compared to baseline stainless steel surface. It was also found that the electron donor component of surface energy would determine the tendency of a surface to foul or not.

Superhydrophilic and oleophobic membrane functionalized with heterogeneously tailored two-dimensional layered double hydroxide nanosheets for antifouling

Fouling is a common challenge to all membrane-based separation technologies. The current study demonstrated an antifouling membrane with a superhydrophilic but oleophobic (in air) characteristic, which was achieved through covalently tethering heterogeneously tailored two-dimensional layered double hydroxide (LDH) nanosheets to a polyvinylidene fluoride membrane surface. The nanosheets were in situ grafted with alternately arranged sodium 1-dodecanesulfonate (SDS) and 3-aminopropyltriethoxysilane (APTS) chains during preparation. Poly(methacrylic acid) (PMAA) was previously grafted on the membrane via plasma induced graft copolymerization as anchor sites for nanosheet binding. With a simple dip-coating operation, the surface-tailored LDH nanosheets could be bound to the membrane via cross-linking between the amine groups of APTS and carboxyl groups of PMAA. Ultimately, the long hydrophobic SDS and short hydrophilic APTS chains on the nanosheets formed a heterogeneous and infiltration selective (due to steric exclusion) surface on the membrane. As a result, the hydrophilic moieties on the membrane surface were much more accessible to water than to liquids of larger molecular size, thereby bringing about the superhydrophilic but oleophobic characteristic. The functionalization gave rise to both significantly enhanced wettability and hydrophilicity of the membrane, mainly owing to the increase of the electron donor component of surface energy (γAB−). Additionally, the functionalized membrane obtained a greater permeability without compromising its selectivity. Furthermore, as verified in both filtration tests with synthetic and practical foulant solutions, the superhydrophilic and oleophobic characteristic endowed the functionalized membrane with conspicuously greater cleaning efficiency and excellent capability in resisting irreversible fouling, suggesting promising applications in various fields.

Innovative non-metal heat transfer surfaces to mitigate crystallization fouling

In this study, non-metal silicon carbide (SiC) substrates were used as non-adhesive heat transfer surfaces to eliminate the negative impacts of crystallization fouling of CaSO4 solutions. The experimental results showed that the SiC substrates, to large extent, were able to mitigate scaling in terms of lower initial fouling rates by as much as four-fold to that of baseline stainless steel (SS) substrates. The superiority can be related to the unique surface characteristic of SiC substrates in terms of higher value of the electron donor component which was 8 times higher than SS surfaces. The post-fouling examination of deposit layers revealed that the layers were very porous where only few number of crystal clusters formed on the surfaces. The deposited crystal clusters, to some extent, were also non-stickable as such that they dropped off the surface completely after each dismantling from the test rig. Larger porous deposit layer on SiC substrates showed also better thermal performance compared to similar tests for the SS substrates. The fouling runs of SiC surfaces showed similar propensity for different surface temperatures, where a reduction of surface temperature by 10 °C resulted in 89% lower initial fouling rate which is noticeable for implementation in industry. The low stickability of the deposit layer on SiC surfaces would implicitly indicate much less hazardous chemical inhibitors and/or cleaning agents would be required to clean the surface from formed deposits.

New insights into the rapid formation of initial membrane fouling after in-situ cleaning in a membrane bioreactor

Abstract In-situ chemical cleaning with sodium hypochlorite (NaClO) is often employed for maintaining constant permeability in a membrane bioreactor (MBR). In this study, the effect of NaClO shock on the rapid formation of initial membrane fouling was investigated over the course of the in-situ cleaning of a MBR. Variations of trans-membrane pressure (TMP) in the different runs indicated that the bulk sludge after NaClO-shock promotes the rapid formation of initial membrane fouling. After in-situ cleaning, the sludge had a high protein content in different extracellular polymeric substance layers and a substantial deterioration in sludge filterability compared to raw sludge. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, NaClO shock significantly changes the surface properties of raw sludge. It reduces the surface electron donor component ( γ − ) and increases surface hydrophobicity. The sludge after NaClO-shock exhibited a stronger adhesive energy with the membrane and higher self-cohesive ability, resulting in severe membrane fouling.

Zn Phthalocyanine Derivatives for Solution‐Processed Small Molecule Organic Solar Cells

AbstractZinc phthalocyanine derivatives, 1 and 2, having either electron donating octyl‐thiol group or electron accepting octyl‐sulfonyl groups have been synthesized to serve as new electron donor components for bulk heterojunction (BHJ) solar cells. BHJ solar cells, in which the active layer consist of zinc phthalocyanine (ZnPc) as an electron donor and a soluble fullerene derivative, namely PCBM, as an electron acceptor component were produced and characterized. The device consisting of octylthiol‐ZnPc:PCBM (1:4) gave power‐conversion efficiencies of 0.42%. On the other hand, the device having octyl‐sulfonyl substituted ZnPc gave very low efficiency due to both low Voc and Jsc values.

Assembly of poly-3-(hexylthiophene) nanocrystals in marginal solvent: The role of PCBM

Poly-3-(hexyl thiophene) (P3HT) represents the benchmark semiconducting polymer for the fabrication of organic photovoltaics (OPVs), where it acts as electron donor component in combination with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), as electron acceptor counterpart. The assembly of P3HT under marginal solvent conditions to form dispersions of fibrillar nanocrystals (NCs) is a particularly attractive method for the subsequent fabrication of highly crystalline films, if compared to depositions involving polymer solutions followed by relatively harsh thermal/solvent treatments, which are often incompatible with sensitive substrates. However, the mechanisms that drive the assembly of P3HT to NCs in marginal solvents are not fully understood, while the effects induced by the presence of PCBM during polymer assembly are still debated. In order to shed light into these processes, we systematically investigated the aggregation/crystallization behaviour of P3HT to NCs under different marginal-solvent conditions and in the presence of different relative contents of PCBM. The starting concentration of P3HT was shown to influence assembly kinetics, the micro-/nano-morphology and the photophysical properties of the formed NCs, as demonstrated by combining atomic force microscopy (AFM) and UV–vis adsorption spectroscopy. Polymer assembly to NCs was also highly dependent on the relative concentration of PCBM, within P3HT:PCBM mixtures typically applied in OPVs. In particular, the combination of UV–vis, AFM and wide-angle X-ray scattering (WAXD) highlighted that PCBM confined the aggregation/crystallization process of P3HT NCs, allowing the formation of extended crystallites, while at high concentrations it hindered the formation of NCs slowing down their assembly.

Bulk Heterojunction Solar Cells: The Role of Alkyl Side Chain on Nanoscale Morphology of Sulfur Over-rich Regioregular Polythiophene/Fullerene Blends

Regioregular HH-TT poly(3,3′-thioalkylbithiophene)s-bearing branched or linear alkyl side-chain substituents (PT2SR) have been synthesized and characterized to investigate their behavior, when used as electron-donor components in blend with a fullerene derivative [[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)] as an electron acceptor, in air-processed photovoltaic solar cells with bulk heterojunction architecture. The optoelectronic characteristics, energy gap, nanoscale morphology, and crystallinity of the blends (PT2SR/PCBM) were examined by ultraviolet–visible spectroscopy, cyclic voltammetry, Kelvin probe force microscopy (KPFM), and X-ray diffraction (XRD). We demonstrate that thioalkyl substituents are able to influence the PCBM self-assembly and the morphology of the polymeric film, important parameters to maximize the efficiency of the solar cell. In particular, the presence of chemical branching in the side chain of the sulfur over-rich polythiophene backbone favors the formation of PCBM clus...

Impact of sodium hypochlorite cleaning on the surface properties and performance of PVDF membranes

Abstract The adverse effect of sodium hypochlorite (NaClO) cleaning has raised concerns regarding their potential impacts on the membrane materials and activated sludge. In this study, the effect of NaClO cleaning on the physicochemical properties, surface free energy, and fouling propensity of polyvinylidene fluoride (PVDF) membranes was systematically investigated. The Analysis of Variance showed that the variation of NaClO soaking time had a significant effect on the permeability and hydrophilicity of PVDF membranes, while effects of NaClO concentration were insignificant. Results showed that the chemical cleaning with NaClO led to a reduction of membrane mechanical strength, which meant the potential harmful impact on the mechanical stability of membranes. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis results showed that the electron donor components (γ−) of membrane surfaces decreased and the electron acceptor components (γ+) relatively increased with the extension of NaClO exposure time, which facilitated membrane fouling propensity.

Ternary Organic Solar Cells with Coumarin7 as the Donor Exhibiting Greater Than 10% Power Conversion Efficiency and a High Fill Factor of 75.

Ternary bulk heterojunction (BHJ) is a brilliant photovoltaic technology for improving the performance of organic solar cells (OSCs), because the light absorption range can be significantly extended by using multiple donors or acceptor materials. In this paper, coumarin7 (C7), a small organic molecule typical led used in organic light-emitting diodes, was initially exploited as second electron-donor component in ternary bulk heterojunction OSCs along with conventional blend system spolythieno[3,4-b]-thiophene/benzodithiophene(PTB7) and [6,6]-phenyl-C71 -butyric acid methyl(PC71 BM). A champion PCE value of 10.28% was realized in the ternary OSCs when incorporated with 10 wt % C7 doping ratio in the donors, corresponding to about 35% enhancement compared with the PTB7:PC71BM-based OSCs, a high fill factor (FF) of 75.03%, a short-circuit currentdensity (Jsc) of 18.72 mA cm-2 and an open-circuit voltage (Voc) of 0.73 V. The enhanced performance of the ternary OSCs can be attributed to the simultaneous improvement of the FF and the Jsc. In addition to extended light absorption, a perfect nanofiber filament active layer morphology is obtained due to the good compatibility between C7 and PTB7, which facilitates the balance of charge transportation and the suppression of charge recombination. This investigation suggests that coumarin derivatives, which have completely different structure with polymer donors, can also be used to fabricate ternary solar cells and have the potential applications to obtain amazing performance after further device engineering and optimization.

Designing Small Molecule Organic Solar Cells with High Open‐Circuit Voltage

AbstractThree extended 2,5‐dithienylthiazolo[5,4‐d]thiazole‐based small molecule chromophores are prepared via a sustainable direct arylation approach and their physicochemical and opto‐electrical material characteristics are analyzed toward integration in solution‐processed bulk heterojunction organic photovoltaics. Efficient charge separation and high values of the charge transfer state energy are derived from sensitive ground and excited state absorption and photoluminescence measurements on blends of the thiazolo[5,4‐d]thiazole‐based electron donor components with the PC71BM fullerene acceptor. Upon implementation in organic solar cells, a maximum power conversion efficiency of 2.7% and particularly high open‐circuit voltages (0.93−0.98 V) are observed, which are correlated to the charge transfer state energies as derived from photoluminescence, Fourier transform photocurrent spectroscopy and combined electrochemical and photophysical data. Furthermore, several loss processes at the origin of the modest short‐circuit current densities and fill factors are elucidated.

Synthesis, characterization and photovoltaic properties of dithienobenzodithiophene-based conjugated polymers

Two new donor-acceptor typed conjugated polymers (P1 and P2) based on the large coplanar and more-extended donor dithieno[2,3-d:2,3-d′]benzo[1,2-b:4,5-b′]dithiphene and thienopyrroledione (TPD) units were synthesized. P1 and P2 have the same polymer backbone, but with different side chains, where P1 has 2-ethylhexyl side chains and P2 has the longer branched 4-ethyoctyl side chains. The solubility measurements show that P2 with longer branched 4-ethyloctyl side chain has better solubility in organic solvents than that of P1. The optical, electrochemical and photovoltaic properties were investigated. P1 and P2 show the very same absorption features in both solution and film states indicating an enhanced molecular planarity of the polymer chains in P1 and P2, which benefits from the large coplanar dithieno[2,3-d:2,3-d′]benzo[1,2-b:4,5-b′]dithiphene unit. The band-gaps of P1 and P2 are at 1.83 eV and 1.74 eV, respectively. The solar cells with P1 or P2 as the electron donor component and PC71BM as the electron acceptor were fabricated and measured under AM 1.5G illumination at 100 mW cm−2. The results show that the P2/PC71BM-based device showed a moderate power conversion efficiency of 2.86%, which is ∼50% improvement in comparison with P1/PC71BM-based device.

Surface Properties of Ti-6Al-4V Alloy: Part II: DPPC Monolayer and Bilayer Deposition in Aspect of Wettability

Phospholipids as the principal constituents of biological cell membranes play important roles in cell communication, signal transportation and various intra- and extra-cellular processes. Therefore, they could be prospective modifier for Ti-6Al–4V alloy used as implants. In this research, 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer or bilayer were deposited on the titanium plate surface using Langmuir-Blodgett and Langmuir-Schaefer (LB/LS) techniques, and spreading method to investigate the change of the surface wettability caused by the deposition. Simultaneously the surface topography was investigated by optical profilometer and atomic force microscopy (AFM). The wettability was investigated by measurement of advancing and receding contact angles of water, formamide and diiodomethane on the deposited DPPC monolayer and bilayer surfaces. Then the surface free energy was calculated applying four approaches, i.e. Lifshitz-van der Waals/Acid Base (LWAB), Contact Angle Hysteresis (CAH), Owens-Wendt (O-W) and Neumann’s equation of state (Eq.State). It is obvious that the films prepared by LB/LS technique are uniform and well-packed, just opposite to those obtained by spreading. This reflects in the surface free energy, which is higher of the DPPC films produced by spreading than by LB/LS technique, which is probably caused by exposure of more DPPC hydrophilic groups outward on the Ti-6Al–4V surface. It appeared that total surface free energy of DPPC bilayer were comparable to that of monolayer. This could be explained by reorganization of DPPC molecule in contact with air atmosphere. However, the electron-donor component was larger suggesting that more polar groups were exposed outward on the bilayer than monolayer surface.

Influences of acid–base property of membrane on interfacial interactions related with membrane fouling in a membrane bioreactor based on thermodynamic assessment

Failure of membrane hydrophobicity in predicting membrane fouling requires a more reliable indicator. In this study, influences of membrane acid base (AB) property on interfacial interactions in two different interaction scenarios in a submerged membrane bioreactor (MBR) were studied according to thermodynamic approaches. It was found that both the polyvinylidene fluoride (PVDF) membrane and foulant samples in the MBR had relatively high electron donor (γ−) component and low electron acceptor (γ+) component. For both of interaction scenarios, AB interaction was the major component of the total interaction. The results showed that, the total interaction monotonically decreased with membrane γ−, while was marginally affected by membrane γ+, suggesting that γ− could act as a reliable indicator for membrane fouling prediction. This study suggested that membrane modification for fouling mitigation should orient to improving membrane surface γ− component rather than hydrophilicity.

Techniques to Improve the Efficiency of Bulk Heterojunction Polymer Solar Cells

Polymer solar cells (PSCs) have attracted much attention recently because of their high flexibility, lightweight, low cost, cheap processing technique and future promise of higher power conversion efficiency. With the realization of photo-induced electron transfer from a conjugated polymer to fullerene component, the bulk heterojunction PSC has become the most successful device structure developed in the field of organic solar cells till present day. The efficiency of bulk heterojunction (BHJ) solar cells has increased steadily over the last decade, currently reaching over 10%. The bulk heterojunction solar cells consist of a phase-separated blend of organic electron donor and acceptor components, where the donor component is a conductive polymer and the acceptor component is a fullerene derivative. In order to achieve high performance and efficiency in BHJ PSCs, a wide range of visible light wavelength needs to be absorbed by the electron donating conjugated polymer and at the same time, the conjugated polymer must possess a characteristic good hole mobility. Recent studies have shown new ways and control mechanisms to improve the efficiency of organic PSCs. This study reviews the various techniques used to improve polymer solar cell technology, the device operation mechanism, and the material design requirements. Potential future applications of this technology in flexible and portable devices are also discussed. Figure 1

Evaluation of SICON® surfaces for biofouling mitigation in critical process areas

In industrial processes, particularly in the food sector, sustainability is increasingly important. Consumers demand safer food and this is often associated with elevated cleaning costs and high environmental impacts in order to reduce contaminations on equipment and products.Modified surfaces are seen as a promising strategy for biofouling mitigation and contamination prevention. In this work, the performance of a modified Diamond-Like Carbon (DLC) surface designated by SICON® (a-C:H:Si:O) was compared with stainless steel (316L) regarding bacterial adhesion, biofilm formation and cleanability. Assays were performed at different temperatures using Escherichia coli, one of the most persistent foodborne microorganisms and also the natural flora present in the water from an industrial salad washing line. Bacterial adhesion on SICON® and stainless steel were similar and favored at a higher temperature (30°C). Biofilm formation was reduced on SICON® (1–2Log) and this may be explained by the lower ratio between the Lifshitz-van der Waals apolar component and the electron donor component (γLW/γ−) of this surface. It was also shown that after performing a cleaning treatment with chlorine, reduction of viability counts was much higher in SICON® (about 3.5Log reduction and 15% removal) when compared to stainless steel (1.6 Log reduction and 6% removal). Additionally, it was observed that 18h after treatment, biofilm values in SICON® were similar to those obtained with stainless steel.Results indicate that for industries with cleaning frequencies of up to 6h, the use of SICON® on critical areas enables operation at a much higher hygienic level.

Influence of structural factors and the properties of the medium on the fluorescence of Zn(II)bis(dipyrrinate)s

This paper presents the results of quantum-chemical and spectral studies on studying fluorescence of binuclear zinc(II)–bis(dipyrrinate)s [Zn2L2] in non-polar and polar environments and their binary mixtures. We studied the efficiency of the fluorescence quenching of fluorophores depending on of isomerism forming their bis(dipyrrine) ligands and an electron-donating ability of the solvent. Found that 3,3′-bis(dipyrrinato)zinc(II) demonstrates the highest sensitivity of the fluorescence to the presence of the electron-donor component compared with 2,3′- and 2,2′-analogs. The results obtained allow to offer helicates [Zn2L2] as new, highly sensitive and selective fluorescent sensors for the detection of N- and O-containing analytes.

Influence of Solvation and Structural Contributions on Fluorescence of Dipyrrine Dyes.

The results of quantum-chemical and spectral researches of zinc((II)) complexes with alkylated dipyrrine and 3,3'-, 2,3'- and 2,2'-bis(dipyrrine)s in non-polar and polar solvents and their binary mixtures are presented. It was investigated the efficiency of the fluorescence quenching of fluorophores depending on of the solvation and structural contributions. Found that 3,3'-bis(dipyrrinato)zinc((II)) demonstrates the highest sensitivity of the fluorescence to the presence of the electron-donor component compared with the studied complexes. The obtained results allow to offer dipyrrine and bis(dipyrrine) zinc((II)) complexes as new, highly sensitive and selective fluorescent sensors of the N- and O-containing toxicants. Graphical Abstract Influence of solvation and structural contributions on fluorescence of dipyrrine dyes.

A criterion for the characterization of modified surfaces during crystallization fouling based on electron donor component of surface energy

Surface treatment is gaining increased attention as an environmentally-friendly approach to combat crystallization fouling by minimizing adhesion energies between precursors and the substrate. What specific components of the surface energy cause this to happen though is still a matter of much debate. The present study aims at developing a criterion by identifying what interaction energies and surface energy components would cause a surface to foul. The proposed criterion shows that the Lewis acid-base interaction energy has a strong implication on the adhesion process. Most notably, increased Lewis base polarity component provides a higher repulsive energy, which in turn reduces the adhesion force between precursors and the substrate. The criterion was validated with the experimental data of this study and some previous studies of crystallization- and bio-fouling which showed that the tendency of surfaces to foul decreases when the electron donor component increases.

Linear and propeller-like fluoro-isoindigo based donor–acceptor small molecules for organic solar cells

Two donor–acceptor type fluoro-isoindigo based small molecule semiconductors are synthesized and their optical, electrochemical, thermal, and charge transport properties are investigated. The two molecular chromophores differ by their architecture, linear (M1) vs propeller-like (M2). Both molecules present a broad absorption in the visible range and a low optical HOMO–LUMO gap (∼1.6eV). AFM images of solution-processed thin films show that the trigonal molecule M2 forms highly oriented fibrils after a few seconds of solvent vapor annealing. The materials are evaluated as electron donor components in bulk heterojunction organic solar cells using PC61BM as the electron acceptor. The devices based on the propeller-like molecule M2 exhibit a high open-circuit voltage (around 1.0V) and a power conversion efficiency of 2.23%.