ABSTRACT
Lately, carbazole-based self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). Nevertheless, these SAMs tend to aggregate in solvents due to their amphiphilic nature, hindering the formation of a monolayer on the ITO substrate and impeding effective passivation of deep defects in the perovskites. In this study, a series of new SAMs including DPA-B-PY, CBZ-B-PY, POZ-B-PY, POZ-PY, POZ-T-PY, and POZ-BT-PY are synthesized, which are employed as interfacial repairers and coated atop CNph SAM to form a robust CNph SAM@pseudo-planar monolayer as HSL in efficient inverted PSCs. The CNph SAM@pseudo-planar monolayer strategy enables a well-aligned interface with perovskites, synergistically promoting perovskite crystal growth, improving charge extraction/transport, and minimizing nonradiative interfacial recombination loss. As a result, the POZ-BT-PY-modified PSC realizes an impressively enhanced solar efficiency of up to 24.45% together with a fill factor of 82.63%. Furthermore, a wide bandgap PSC achieving over 19% efficiency. Upon treatment with the CNph SAM@pseudo-planar monolayer, also demonstrates a non-fullerene organic photovoltaics (OPVs) based on the PM6:BTP-eC9 blend, which achieves an efficiency of 17.07%. Importantly, these modified PSCs and OPVs all show remarkably improved stability under various testing conditions compared to their control counterparts.
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Fish mint, Houttuynia cordata Thunb. (HCT) is an edible vegetable that has also been used in traditional folk medicines. As both a medicinal herb and a dietary source, HCT has been clinically proven to be a pivotal ingredient in formulas administered to alleviate COVID-19 symptoms. With the increasing market demand for imported materials, ensuring the quality consistency of HCT becomes a significant concern. In this study, the growing time for hydroponically-cultivated HCT with seaweed extract and amino acids added (HCTW) reduced by half compared to conventional soil-cultivated HCT (HCTS). Key quantified components in HCTW, flavonoid glycosides and caffeoylquinic acid derivatives, exhibited a 143% increase over HCTS. These crucial constituents were responsible for possessing antioxidant activity (IC50 < 25 µg/mL) and anti-nitrite oxide production (IC50 < 20 µg/mL). An economically-designed hydroponic system with appropriate additives is proposed to replace HCTS with improvements of growth time, overall production yields, and bioactive qualities.
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BACKGROUND: Non-invasive techniques such as central intermittent theta burst stimulation (iTBS) and repetitive peripheral magnetic stimulation (rPMS) have shown promise in improving motor function for patients with stroke. However, the combined efficacy of rPMS and central iTBS has not been extensively studied. This randomized controlled trial aimed to investigate the synergistic effects of rPMS and central iTBS in patients with stroke. METHOD: In this study, 28 stroke patients were randomly allocated to receive either 1200 pulses of real or sham rPMS on the radial nerve of the affected limb, followed by 1200 pulses of central iTBS on the ipsilesional hemisphere. The patients received the intervention for 10 sessions over two weeks. The primary outcome measures were the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) and the Action Research Arm Test (ARAT). Secondary outcomes for activities and participation included the Functional Independence Measure-Selfcare (FIM-Selfcare) and the Stroke Impact Scale (SIS). The outcome measures were assessed before and after the intervention. RESULTS: Both groups showed significant improvement in FMA-UE and FIM-Selfcare after the intervention (p < 0.05). Only the rPMS + iTBS group had significant improvement in ARAT-Grasp and SIS-Strength and activity of daily living (p < 0.05). However, the change scores in all outcome measures did not differ between two groups. CONCLUSIONS: Overall, the study's findings suggest that rPMS may have a synergistic effect on central iTBS to improve grasp function and participation. In conclusion, these findings highlight the potential of rPMS as an adjuvant therapy for central iTBS in stroke rehabilitation. Further large-scale studies are needed to fully explore the synergistic effects of rPMS on central iTBS. TRIAL REGISTRATION: This trial was registered under ClinicalTrials.gov ID No.NCT04265365, retrospectively registered, on February 11, 2020.
Subject(s)
Stroke Rehabilitation , Stroke , Humans , Magnetic Phenomena , Stroke Rehabilitation/methods , Transcranial Magnetic Stimulation/methods , Treatment Outcome , Upper Extremity , Double-Blind MethodABSTRACT
Tubulin beta 4A class IVa (TUBB4A) spectrum disorders include autosomal dominant dystonia type 4 or hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC syndrome). However, in rare cases, only mild hypomyelination in the cortex with no basal ganglia atrophy may be observed. We report a case of a family with TUBB4A mutation and complicated hereditary spasticity paraplegia (HSP). We performed quadro whole-exome sequencing (WES) on the family to identify the causative gene of progressive spastic paraparesis with isolated hypomyelination leukodystrophy. We identified a novel TUBB4A p.F341L mutation, which was present in all three affected patients but absent in the unaffected father. The affected patients presented with adult-onset TUBB4A disorder, predominant spastic paraparesis with/without ataxia, and brain hypomyelination with no cognitive impairment or extrapyramidal symptoms. In the literature, HSP is considered a TUBB4A spectrum disorder.
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Self-assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis of a new series of carboxylic acid-functionalized porphyrin derivatives, namely AC-1, AC-3, and AC-5, and present, for the first time, a strategy to exploit the large π-moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron-rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects. Comprehensive spectroscopic and dynamic studies demonstrate that the double-anchored AC-3 and AC-5 enhance SAMs on ITO, passivate the perovskite layer, and function as conduits to facilitate hole transfer, thus significantly boosting the performance of PSCs. The champion inverted PSC employing AC-5 SAM achieves an impressive solar efficiency of 23.19 % with a high fill factor of 84.05 %. This work presents a novel molecular engineering strategy for functionalizing SAMs to tune the energy levels, molecular dipoles, packing orientations to achieve stable and efficient solar performance. Importantly, our comprehensive investigation has unraveled the associated mechanisms, offering valuable insights for future advancements in PSCs.
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Inverted perovskite solar cells (PSCs) have attracted intense attention because of their insignificant hysteresis and low-temperature fabrication process. However, the efficiencies of inverted PSCs are still inferior to those of commercialized silicon solar cells. Also, the poor stability of PSCs is one of the major impedances to commercialization. Herein, we rationally designed and synthesized a new series of electron donor (R,R-diphenylamino) and acceptor (pyridimium-(CH2) n -sulfonates) zwitterions as a boundary modulator and systematically investigated their associated interface properties. Comprehensive physical and optoelectronic studies verify that these zwitterions provide a four-in-one functionality: balancing charge carrier transport, suppressing less-coordinated Pb2+ defects, enhancing moisture resistance, and reducing ion migration. Although each functionality may have been reported by specific passivating molecules, a strategy that simultaneously regulates the charge-transfer balance and three other functionalities has not yet been developed. The results are to make an omnidirectional improvement of PSCs. Among all zwitterions, 4-(4-(4-(di-(4-methoxylphenyl)amino)phenyl)propane-1-ium-1-yl)butane-1-sulfonate (OMeZC3) optimizes the balance hole/electron mobility ratio of perovskite to 0.91, and the corresponding PSCs demonstrate a high power conversion efficiency (PCE) of up to 23.15% free from hysteresis, standing out as one of the champion PSCs with an inverted structure. Importantly, the OMeZC3-modified PSC exhibits excellent long-term stability, maintaining almost its initial PCE after being stored at 80% relative humidity for 35 days.
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This study aimed to investigate the effects of different tools and working heights on physical workloads in vertical cleaning tasks. Thirty healthy adults were recruited to use a rag and a long-handle tool (LHT) to simulate cleaning operations on the Wii Fit board surfaces of 3 different heights, respectively. Participants used a lower 50th percentile force but were required to spend a longer time to finish the task while using an LHT than using a rag. The tool preferences were the main factors considered for efficiency and personal subjective workload and physiological load. 76.6% of the participants preferred to use the LHT instead of the rag at a high task height, but 70% preferred to use the rag when working at a medium task height. For low workload cleaning tasks on vertical surfaces, employers should provide cleaners with different handle lengths tools to choose from to reduce the cleaner's workload.
Subject(s)
Task Performance and Analysis , Workload , Adult , HumansABSTRACT
Movement disorders are common manifestations in autoimmune-mediated encephalitis. This group of diseases is suspected to be triggered by infection or neoplasm. Certain phenotypes correlate with specific autoantibody-related neurological disorders, such as orofacial-lingual dyskinesia with N-methyl-D-aspartate receptor encephalitis and faciobrachial dystonic seizures with leucine-rich glioma-inactivated protein 1 encephalitis. Early diagnosis and treatment, especially for autoantibodies targeting neuronal surface antigens, can improve prognosis. In contrast, the presence of autoantibodies against intracellular neuronal agents warrants screening for underlying malignancy. However, early clinical diagnosis is challenging because these diseases can be misdiagnosed. In this article, we review the distinctive clinical phenotypes, magnetic resonance imaging findings, and current treatment options for autoimmune-mediated encephalitis.
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Nanoparticle-mineral surface interactions are relevant in many biological and geological applications. We have previously studied nanoparticle coatings based on closely packed bicomponent polyol-fluoroalkane self-assembled monolayers (SAMs) that can have tunable stickiness on calcite surfaces by changing the compositions of fluoroalkanes in SAMs, where the coatings show nonstick properties if fluoroalkanes can effectively perturb hydration layers on calcite surfaces. However, when applying coatings on nanoparticles, it can be challenging to predict the maximum achievable coating density. Here, we study how would water-mediated SAM-calcite interactions change with different SAM coating densities. Molecular dynamics simulations show that compositionally repulsive, closely packed polyol-fluoroalkane SAMs become adhesive to calcite surfaces with decreasing coating densities. Our modeling shows that this results from the collapsing of fluoroalkanes into the voids of SAMs, where fluoroalkanes can no longer perturb hydration layers on calcite surfaces. Interestingly, we find that the nonstick-stick transition occurs when the volume fractions of the voids on SAMs are greater than the volume fractions of hydrophilic coating molecules.
Subject(s)
Molecular Dynamics Simulation , Water , Hydrophobic and Hydrophilic InteractionsABSTRACT
BACKGROUND: Virtual reality and arm cycling have been reported as effective treatments for improving upper limb motor recovery in patients with stroke. Intermittent theta burst stimulation (iTBS) can increase ipsilesional cortical excitability, and has been increasingly used in patients with stroke. However, few studies examined the augmented effect of iTBS on neurorehabilitation program. In this study, we investigated the augmented effect of iTBS on virtual reality-based cycling training (VCT) for upper limb function in patients with stroke. METHODS: In this randomized controlled trial, 23 patients with stroke were recruited. Each patient received either 15 sessions of iTBS or sham stimulation in addition to VCT on the same day. Outcome measures were assessed before and after the intervention. Primary outcome measures for the improvement of upper limb motor function and spasticity were Fugl-Meyer Assessment-Upper Extremity (FMA-UE) and Modified Ashworth Scale Upper-Extremity (MAS-UE). Secondary outcome measures for activity and participation were Action Research Arm Test (ARAT), Nine Hole Peg Test (NHPT), Box and Block Test (BBT) and Motor Activity Log (MAL), and Stroke Impact Scale (SIS). Wilcoxon signed-rank tests were performed to evaluate the effectiveness after the intervention and Mann-Whitney U tests were conducted to compare the therapeutic effects between two groups. RESULTS: At post-treatment, both groups showed significant improvement in FMA-UE and ARAT, while only the iTBS + VCT group demonstrated significant improvement in MAS-UE, BBT, NHPT, MAL and SIS. The Mann-Whitney U tests revealed that the iTBS + VCT group has presented greater improvement than the sham group significantly in MAS-UE, MAL-AOU and SIS. However, there were no significant differences in the changes of the FMA-UE, ARAT, BBT, NHPT and MAL-QOM between groups. CONCLUSIONS: Intermittent TBS showed augmented efficacy on VCT for reducing spasticity, increasing actual use of the affected upper limb, and improving participation in daily life in stroke patients. This study provided an integrated innovative intervention, which may be a promising therapy to improve upper limb function recovery in stroke rehabilitation. However, this study has a small sample size, and thus a further larger-scale study is warranted to confirm the treatment efficacy. Trial registration This trial was registered under ClinicalTrials.gov ID No. NCT03350087, retrospectively registered, on November 22, 2017.
Subject(s)
Stroke Rehabilitation , Stroke , Virtual Reality , Humans , Recovery of Function , Stroke/complications , Transcranial Magnetic Stimulation , Treatment Outcome , Upper ExtremityABSTRACT
Using hydrodynamic simulations, we study the single polymers flowing through model porous media (close-packed colloidal crystal). In good solvent or high flow rates, the polymer transport is similar to gel electrophoresis, with size-dependent sieving for L_{c}/Lâ²1 and size-independent biased reptation for L_{c}/Lâ³1 (L_{c} is the polymer contour length and L is the diameter of colloids forming the porous media). Importantly, in bad solvent and low flow rates, the polymers show an extra window of size-dependent velocity for 1â²L_{c}/Lâ²2, where the polymer transport is controlled by a globule-stretch transition at pore throats, and the transport velocity is much slower than reptation.
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Engineered nanoparticles have been broadly used in biological and geological systems. Hydrophilic molecules such as polyols have been used as coatings on nanoparticle surfaces due to their good biocompatibility and solubility in saline water. However, polyol coatings can cause huge retention of nanoparticles when encountering mineral surfaces. Here, molecular dynamics simulations enlightened that the strong adhesion of hydrophilic coatings to mineral surfaces stemming from the partitioning of the hydroxy groups on the hydrophilic molecules to the well-defined bound hydration layers on the mineral surfaces. To mitigate the nanoparticle adhesion, we investigated introducing small percentages of omniphobic fluoroalkanes to form a bicomponent system of hydrophilic and fluoroalkanes, which greatly perturbed the hydration layers on mineral surfaces and resulted in nonstick surface coatings. Our results provide important insight for the design of tunable "stickiness" nanoparticle coatings in different mineralogies, such as applications in subsurface environments or targeted delivery in mineralized tissues.
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Efficient control of the perovskite crystallization and passivation of the defects at the surface and grain boundaries of perovskite films have turned into the most important strategies to restrain charge recombination toward high-performance and long-term stability of perovskite solar cells (PSCs). In this paper, we employed a small amount of natural vitamin B (carnitine) with dual functional groups in the MAPbI3 precursor solution to simultaneously passivate the positive- and negative-charged ionic defects, which would be beneficial for charge transport in the PSCs. In addition, such methodology can efficiently ameliorate crystallinity with texture, better film morphology, high surface coverage, and longer charge carrier lifetime, as well as induce preferable energy level alignment. Benefiting from these advantages, the power conversion efficiency of PSCs significantly increases from 16.43 to 20.12% along with not only a higher open-circuit voltage of 1.12 V but also an outstanding fill factor of 82.78%.
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BACKGROUND: Colorectal cancer screening by fecal occult blood testing has been an important public health test and shown to reduce colorectal cancer-related mortality. However, the low participation rate in colorectal cancer screening by the general public remains a problematic public health issue. This fact could be attributed to the complex and unpleasant operation of the screening tool. OBJECTIVE: This study aimed to validate a novel toilet paper-based point-of-care test (ie, JustWipe) as a public health instrument to detect fecal occult blood and provide detailed results from the evaluation of the analytic characteristics in the clinical validation. METHODS: The mechanism of fecal specimen collection by the toilet-paper device was verified with repeatability and reproducibility tests. We also evaluated the analytical characteristics of the test reagents. For clinical validation, we conducted comparisons between JustWipe and other fecal occult blood tests. The first comparison was between JustWipe and typical fecal occult blood testing in a central laboratory setting with 70 fecal specimens from the hospital. For the second comparison, a total of 58 volunteers were recruited, and JustWipe was compared with the commercially available Hemoccult SENSA in a point-of-care setting. RESULTS: Adequate amounts of fecal specimens were collected using the toilet-paper device with small day-to-day and person-to-person variations. The limit of detection of the test reagent was evaluated to be 3.75 µg of hemoglobin per milliliter of reagent. Moreover, the test reagent also showed high repeatability (100%) on different days and high reproducibility (>96%) among different users. The overall agreement between JustWipe and a typical fecal occult blood test in a central laboratory setting was 82.9%. In the setting of point-of-care tests, the overall agreement between JustWipe and Hemoccult SENSA was 89.7%. Moreover, the usability questionnaire showed that the novel test tool had high scores in operation friendliness (87.3/100), ease of reading results (97.4/100), and information usefulness (96.1/100). CONCLUSIONS: We developed and validated a toilet paper-based fecal occult blood test for use as a point-of-care test for the rapid (in 60 seconds) and easy testing of fecal occult blood. These favorable characteristics render it a promising tool for colorectal cancer screening as a public health instrument.
Subject(s)
Bathroom Equipment/supply & distribution , Colorectal Neoplasms/diagnosis , Mass Screening/methods , Occult Blood , Point-of-Care Testing/standards , Female , Humans , Male , Middle Aged , Reproducibility of Results , Surveys and Questionnaires , VolunteersABSTRACT
BACKGROUND: Recent years have witnessed wide applications of exergames to balance training among the older adults. However, research concerning balance training with the use of Kinect for Xbox has remained scarce. While previous studies have shown the positive effects of exergames on improving balance and preventing falling among the older adults, there has been a paucity of empirical evidence supporting the superiority of Kinect exercise to conventional exercise over balance training among the older adults. Therefore, this study aimed to compare the feasibility, safety, and effectiveness of Kinect exercise against conventional exercise over balance training among the community older adults. METHOD: A total of 20 participants were randomly assigned to the Kinect Exercise Group (Nâ=â10) or the Conventional Exercise Group (Nâ=â10) for a 5-week balance training (45âminutes a time, 2 times a week). Assessor blinding was employed to assess the participants' performance before and after the treatment, including 30-Second Chair Stand Test (30-sec CST), Timed Up and Go (TUG), Functional Reach Test (FRT), and One-Leg Stance Test (OLST) respectively with eyes open and closed. Subjective feeling of the intensity of pain and side effects were recorded throughout the investigation period. Nonparametric statistics was used for data analysis. RESULTS: Within-group comparison between the pre-test and post-test indicated that significant differences existed in all of the 5 tests (30-sec CST, TUG, FRT, OLST with eyes open, and OLST with eyes closed) in the Kinect exercise group. To the Conventional exercise group, however, significant differences were only observed in 30-sec CST, FRT and OLST with eyes open. With regard to between-group comparison, significant differences were only found in FRT. CONCLUSION: Such results indicated that both treatments were helpful in improving the participants' balance performance, that Kinect exercise was more effective in terms of overall balance ability, and that Kinect exercise was particularly beneficial to functional reach enhancement in comparison with traditional exercise. Kinect exercise could be a feasible, safe, and effective alternative for dynamic balance training among older adults.
Subject(s)
Accidental Falls/prevention & control , Exercise Therapy/methods , Postural Balance/physiology , Video Games , Aged , Feasibility Studies , Female , Humans , Independent Living , Male , Middle Aged , Single-Blind Method , Treatment OutcomeABSTRACT
PURPOSE: To examine the responsiveness and minimal clinically important difference (MCID) of the TNO-AZL (Netherlands Organization for Applied Scientific Research Academic Medical Centre) Preschool Children Quality of Life (TAPQOL) in children with cerebral palsy (CP). METHODS: Ninety-seven children with CP (60 males, 37 females; aged 1-6 years) and their caregivers were recruited from the rehabilitation programs of Chang Gung Memorial Hospital in Taiwan for this 6-month longitudinal follow-up study. The Functional Independence Measure for Children (WeeFIM) and TAPQOL outcomes were measured at baseline and at a 6-month follow-up. Responsiveness was examined using the standardized response mean (SRM). The distribution-based and anchor-based MCID were determined. The TAPQOL outcomes include physical functioning (PF), social functioning (SF), cognitive functioning (CF), and emotional functioning (EF) domains. RESULTS: The responsiveness of the TAPQOL for all of TAPQOL domains was marked (SRM = 1.12-1.54). The anchor-based MCIDs of TAPQOL for PF, SF, CF, EF, and total domains were 1.25, 3.28, 2.93, 2.25, and 1.73, respectively, which were similar to the distribution-based MCID values of TAPQOL, except in the PF domain. The distribution-based MCIDs of TAPQOL in various domains were 2.85-3.73 when effect size (ES) was 0.2, 7.13-9.32 when ES was 0.5, and 11.40-14.91 when ES was 0.8. CONCLUSIONS: TAPQOL is markedly responsive to detect change in children with CP. The caregivers perceived the minimally important change in HRQOL of their children at a relatively low treatment efficacy. Researchers and clinicians can utilize TAPQOL data to determine whether changes in TAPQOL scores indicate clinically meaningful effects post-treatment and at the follow-up.
Subject(s)
Cerebral Palsy/psychology , Cognition/physiology , Minimal Clinically Important Difference , Physical Functional Performance , Quality of Life/psychology , Caregivers , Child , Child, Preschool , Female , Follow-Up Studies , Humans , Infant , Male , Netherlands , Taiwan , Treatment OutcomeABSTRACT
Alkylbenzene sulfonates are one of the most important synthetic surfactant families, considering their wide applicability, cost-effectiveness, and overall consumption levels. Nevertheless, their low salt tolerance (especially divalent ion contents) prevented their wider applications such as enhanced oil recovery in high salinity reservoirs. Here, using experiments and atomistic molecular dynamics simulations, we demonstrated that the high salinity colloidal stability of alkylbenzene sulfonates can be dramatically increased by mixing with zwitterionic cosurfactants in oil-swollen micelles. By mixing with cosurfactants we had two important observations. (1) The polydispersity of surfactant mixture oil-swollen micelles were largely decreased due to the less rigid oil/water interfaces with mixed surfactants, which formed fewer but larger uniform micelles. (2) Strong dehydration of sulfonates due to the shielding from protruding more extended zwitterionic cosurfactants at the oil/water interfaces. Both observed molecular assembly characteristics triggered by the cosurfactants effectively reduced the total exposures of sulfonates to water phase that may form divalent ion bridging and large aggregates, and thus increased their high salinity colloidal stability. Lastly, it was observed that the dehydration of sulfonates was the highest at flat oil/water interfaces (very large oil-swollen micelles), which justified that adding trace amount of mineral oils may boost the high salinity colloidal stability even further.
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The relative stability constants of Tb(III) complexes exhibiting binding to a series of 4-substituted analogues of dipicolinic acid (2,6-pyridinedicarboxylic acid) (DPA) were calculated using density functional theory (DFT) with the standard thermodynamic cycle. DFT calculations showed that the strengths of the stability constants were modified by the substituents in the following (decreasing) order: -NH2 > -OH â¼ -CH2OH > -imidazole â¼ -Cl â¼ -Br â¼ -H > -F > -I, with the differences among them falling within one to two log units except for -NH2. Through population and structural analysis, we observed that the -NH2, -OH, -CH2OH, and halide substituents can donate electrons via resonance effect to the pyridine ring of DPA while inductively withdrawing electrons with different strengths, thus resulting in the different binding strengths of the 4-substituted DPAs to the Tb(III) ions. We believe that these observations possess utility not only in the ongoing development of luminescent probes for bioanalytical studies but also for more recent cross-industrial efforts to enhance reservoir surveillance capabilities using chemical tracers within the oil and gas sector.
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A series of tailor-made highly efficient and near-infrared (NIR) porphyrin-based acceptors is designed and synthesized for fullerene-free bulk-heterojunction (BHJ) organic solar cells. Constructing BHJ active layers using a PTB7-Th donor and porphyrin acceptors (P-x), which have complementary absorption, accomplishes panchromatic photon-to-current conversion from 300 to 950 nm. Our study shows that side chains of the porphyrin acceptors fairly influence the molecular ordering and nanomorphology of the BHJ active layers. Significantly, the porphyrin acceptor with four dodecoxyl side chains (P-2) achieves an open-circuit voltage (VOC) of 0.80 V, short-circuit current density (JSC) of 13.94 mA cm-2, fill factor of 64.8%, and overall power conversion efficiency of 7.23%. This great performance is attributable to the ascendant light-harvesting capability in the visible and near-infrared region, a high-lying LUMO energy level, a relatively high and more balanced carrier mobilities, and more ordered face-on molecular packing, which is beneficial for obtaining high VOC and JSC.
ABSTRACT
Interest in nanomaterials for subsurface applications has grown markedly due to their successful application in a variety of disciplines, such as biotechnology and medicine. Nevertheless, nanotechnology application in the petroleum industry presents greater challenges to implementation because of the harsh conditions (i.e. high temperature, high pressure, and high salinity) that exist in the subsurface that far exceed those present in biological applications. The most common subsurface nanomaterial failures include colloidal instability (aggregation) and sticking to mineral surfaces (irreversible retention). We previously reported an atomic force microscopy (AFM) study on the calcium-mediated adhesion of nanomaterials in reservoir fluids (S. L. Eichmann and N. A. Burnham, Sci. Rep. 7, 11613, 2017), where we discovered that the functionalized and bare AFM tips showed mitigated adhesion forces in calcium ion rich fluids. Herein, molecular dynamics reveal the molecular-level details in the AFM experiments. Special attention was given to the carboxylate-functionalized AFM tips because of their prominent ion-specific effects. The simulation results unambiguously demonstrated that in calcium ion rich fluids, the strong carboxylate-calcium ion complexes prevented direct carboxylate-calcite interactions, thus lowering the AFM adhesion forces. We performed the force measurement simulations on five representative calcite crystallographic surfaces and observed that the adhesion forces were about two to three fold higher in the calcium ion deficient fluids compared to the calcium ion rich fluids for all calcite surfaces. Moreover, in calcium ion deficient fluids, the adhesion forces were significantly stronger on the calcite surfaces with higher calcium ion exposures. This indicated that the interactions between the functionalized AFM tips and the calcite surfaces were mainly through carboxylate interactions with the calcium ions on calcite surfaces. Finally, when analyzing the order parameters of the tethered functional groups, we observed significantly different behavior of the alkanethiols depending on the absence or presence of calcium ions. These observations agreed well with AFM experiments and provided new insights for the competing carboxylate/calcite/calcium ion interactions.