Thanks to the nature of molecular orbitals, the absorption spectra of organic semiconductors are not continuous like those in traditional inorganic semiconductors, which offers a unique application ...of organic photovoltaics (OPVs): semitransparent OPVs. Recently, the exciting progress of materials design has promoted the development of semitransparent OPVs. However, in the perspective of device engineering, almost all reported works reduce the thickness of back/reflected electrode to obtain high average visible transmittance (AVT), which is a trade‐off between power conversion efficiency (PCE) and the transmittance of the whole solar spectrum (visible and infrared), and therefore limit the further development. Herein, a unique strategy of “transparent hole‐transporting frameworks” is proposed. A hole‐transporting large‐bandgap polymer (polybis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA)) is employed to partially replace polymer donors in the active layer of PBDB‐T/Y1. PTAA is a p‐type polymer with a large bandgap of 2.9 eV; the partial substitution of PBDB‐T by PTAA reduces the absorption of the active layer only in the visible region, keeping the hole‐transporting pathways as well as the optimized film morphology. As a result, semitransparent OPVs with PCEs of 12% and AVTs of 20% are achieved, both on rigid and flexible substrates. To demonstrate the generality, this strategy is also used in three different active layers.
A unique strategy of “transparent hole‐transporting frameworks” is proposed. A hole‐transporting large‐bandgap polymer, PTAA, is employed to partially replace the polymer donors in the active layer. As a result, semitransparent organic photovoltaic devices with power conversion efficiencies ≈12% and average visible transmittances ≈20% are achieved both on rigid and flexible substrates.
Semitransparent organic photovoltaics (ST‐OPVs) have great potential for use in renewable energy technologies. In bulk‐heterojunction (BHJ) ST‐OPVs, a compromise is necessary between the visible ...light transmittance (VLT) and the power conversion efficiency (PCE). A sequential deposition (SD) strategy that involves individually depositing a polymer donor layer (D) and a small‐molecule acceptor layer (A) as the active layer is presented; where molecular diffusion occurring at the interfacial region results in a pseudo p–i–n structure. PBDB‐T‐2F(D)/Y6(A) ST‐OPVs are fabricated with different active layer thicknesses—at 115 nm, the SD (D:A/75:40 nm) and BHJ devices (D:A/1:1.2 w) provide the champion PCE of 12.91% (VLT of 14.5%) and 12.77% (VLT of 13.4%), respectively; at 85 nm, the SD (D:A/45:40 nm) and BHJ devices (D:A/1:1.2 w) provide a PCE of 12.22% (VLT of 22.2%) and 11.23% (VLT of 16.6%), respectively. This trend indicates SD devices have larger PCE and VLT values than the BHJ devices at a given active layer thickness, and the enhancements of PCE and VLT values by the SD structures against the BHJ structures become more pronounced as the active layer thickness reduced. The SD strategy provides a new approach for achieving ST‐OPVs with both high efficiency and high transparency.
In typical semitransparent organic photovoltaics (ST‐OPVs) that incorporate bulk heterojunction (BHJ) active layers, a compromise is made between the visible light transmittance (VLT) and power conversion efficiency (PCE). A new strategy with a sequential‐deposition (SD) active layer involving pseudo p–i–n structures provides ST‐OPVs with simultaneously higher PCE and VLT than that of the BHJ devices at the same layer thickness.
In tandem organic photovoltaics, the front subcell is based on large‐bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a ...narrow‐bandgap acceptor for infrared absorption but a large‐bandgap donor to realize a high open‐circuit voltage. Unfortunately, most of the ultraviolet–visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large‐bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole‐transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared‐absorbing polymer donor as a third component is introduced, which provides a second hole‐generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short‐circuit current density of the two‐terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7 mA cm−2 (while retaining the open‐circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.
In tandem organic photovoltaics, most ultraviolet–visible photons are absorbed by the front sub‐cell, so in the rear sub‐cell, excitons generated on large‐bandgap donors will be reduced significantly. This reduces the conductivity and limits the hole‐transporting property of the rear sub‐cell. An infrared‐absorbing polymer donor is introduced, which provides a second hole‐generation/transporting mechanism to minimize the aforementioned detrimental effects.
This paper reports two new fluorine-substituted polymer donors (BO2FC8, BO2FEH), with different side-chain architectures, and a new chlorine-substituted small-molecule acceptor ( m -ITIC-OR-4Cl) that ...are capable of simultaneous charge and energy transfer as the binary blend active layer for organic photovoltaics. We first resolved the single-crystal structure of m -ITIC-OR-4Cl and then used simultaneous grazing-incidence wide- and small-angle X-ray scattering to decipher the multi-length-scale structures—such as the shape and size of aggregated domains and molecular orientation—of the blends of BO2FEH and BO2FC8 with m -ITIC-OR-4Cl. The linear side chains of BO2FC8 facilitated its packing and, thus, induced m -ITIC-OR-4Cl to form smaller disc-shaped aggregated domains (thickness: 2.9 nm) than its aggregate domain (thickness: 5.4 nm) in the blend of the branched BO2FEH. That is, the binary blend system of linear-side-chain BO2FC8 with m -ITIC-OR-4Cl featured larger interfacial areas and more pathways for charge transfer and transport, as evidenced by their carrier mobilities. The highest power conversion efficiency (PCE) of 11.0% was that for the BO2FC8: m -ITIC-OR-4Cl device, being consistent with the predicted PCE of 11.2% using machine learning based on random forest algorism; in comparison, the PCE of the BO2FEH: m -ITIC-OR-4Cl device was 6.4%. This study has not only provided insight into the photovoltaic performances of new polymer donor/small-molecule acceptor blends but has also, for the first time, deciphered the hierarchical morphologies—from molecule orientation to nano-domain shape and size—of such blend systems, linking the morphologies to the photovoltaic performances. The use of side-chain architectures suggests an approach for tuning the morphology of the polymer/small-molecule binary blend active layer for use in organic photovoltaics.
A new terpolymer acceptor is presented, comprising various ratios of the same dithienothienopyrrolobenzothiadiazole (BTP) core with different side chains—alkoxy side chains (BTPO‐IC) and alkyl side ...chains (BTP‐IC)—and thiophene units, for use in all‐polymer organic photovoltaics. Devices incorporating binary blends of this terpolymer and the polymer PM6 as the active layer displayed open‐circuit voltages (VOC) that increase linearly upon increasing the molar ratio of BTPO‐IC. For example, the optimized device incorporating PM6:PY‐0.2OBO (i.e., with 20 mol% of BTPO‐IC) (1:1.2 wt.%) blend, with the smallest domain sizes but largest coherence length and combined face‐on and edge‐on orientation fractions among all blends, have a champion power conversion efficiency (PCE) of 16.7% (VOC = 0.97 V; JSC = 25.2 mA cm−2; FF = 0.68), whereas the device containing a similar blend ratio of the PM6:PY‐OD:PY‐OBO ternary blend (1:0.96:0.24 wt.%) displayed a PCE of 8.6% (VOC = 0.969 V; JSC = 18.7 mA cm−2; FF = 0.48). The device with PM6:PY‐0.2OBO displays better thermal stability than the devices with PM6: PY‐OD or PY‐OBO. Thus, employing terpolymer acceptors with differently functionalized side‐chain units can be an effective approach for simultaneously optimizing the aggregation domain and enhancing the PCEs and thermal stabilities of all‐polymer devices.
Devices featuring a binary blend active layer incorporating a terpolymer acceptor of dithienothienopyrrolobenzothiadiazole core with alkoxy to alkyl side chains ratio at 25% display an open‐circuit voltage of 0.97 V and a power conversion efficiency (PCE) of 16.7%, indicating the modified terpolymer can be effective materials for optimizing the aggregation domains, the PCEs, and the stabilities of all‐polymer devices.
In this paper, we describe a novel algorithm that counts and classifies highway vehicles based on regression analysis. This algorithm requires no explicit segmentation or tracking of individual ...vehicles, which is usually an important part of many existing algorithms. Therefore, this algorithm is particularly useful when there are severe occlusions or vehicle resolution is low, in which extracted features are highly unreliable. There are mainly two contributions in our proposed algorithm. First, a warping method is developed to detect the foreground segments that contain unclassified vehicles. The common used modeling and tracking (e.g., Kalman filtering) of individual vehicles are not required. In order to reduce vehicle distortion caused by the foreshortening effect, a nonuniform mesh grid and a projective transformation are estimated and applied during the warping process. Second, we extract a set of low-level features for each foreground segment and develop a cascaded regression approach to count and classify vehicles directly, which has not been used in the area of intelligent transportation systems. Three different regressors are designed and evaluated. Experiments show that our regression-based algorithm is accurate and robust for poor quality videos, from which many existing algorithms could fail to extract reliable features.
The rapid evolution of technology has given rise to a connected world where billions of devices interact seamlessly, forming what is known as the Internet of Things (IoT). While the IoT offers ...incredible convenience and efficiency, it presents a significant challenge to cybersecurity and is characterized by various power, capacity, and computational process limitations. Machine learning techniques, particularly those encompassing supervised classification techniques, offer a systematic approach to training models using labeled datasets. These techniques enable intrusion detection systems (IDSs) to discern patterns indicative of potential attacks amidst the vast amounts of IoT data. Our investigation delves into various aspects of supervised classification, including feature selection, model training, and evaluation methodologies, to comprehensively evaluate their impact on attack detection effectiveness. The key features selected to improve IDS efficiency and reduce dataset size, thereby decreasing the time required for attack detection, are drawn from the extensive network dataset. This paper introduces an enhanced feature selection method designed to reduce the computational overhead on IoT resources while simultaneously strengthening intrusion detection capabilities within the IoT environment. The experimental results based on the InSDN dataset demonstrate that our proposed methodology achieves the highest accuracy with the fewest number of features and has a low computational cost. Specifically, we attain a 99.99% accuracy with 11 features and a computational time of 0.8599 s.
Binary acceptor alloys based on two A′′-D′A′D′-A′′ small-molecule acceptors having the same core structures and side chains but different conjugation end groups, namely, BTPO-NF and BTPO-F were ...synthesized and blended with the polymer PM6 for forming ternary blends of organic photovoltaics (OPVs) displaying high open-circuit voltages (
V
OC
), power conversion efficiencies (PCEs), and stability. Both BTPO-NF and BTPO-F possessed the same alkoxy chains, which increased the energies of their lowest unoccupied molecular orbitals (LUMOs) and mutual miscibility. After varying the amount of the two acceptor ratios in the ternary-blend system, we found that the optimum device performance could be achieved in the case of alloy acceptors with one major (BTPO-NF) and one minor (BTPO-F) acceptor component; the PM6:BTPO-NF:BTPO-F (1 : 1 : 0.2 wt) ternary-blend device provided the highest PCE of 18.0% with a high
V
OC
of 0.97 V, with the PM6:BTPO-NF and PM6:BTPO-F (1 : 1.2 wt) devices displaying PCEs of 17.11% and 16.23, respectively. The enhancement in the PCE value of the PM6:BTPO-NF:BTPO-F (1 : 1 : 0.2 wt) ternary-blend device resulted from the increase in the photocurrent of the device with the optimized active layer morphology induced by the alloy acceptor structures as compared to that of the binary-blend devices. Thus, the strategy of molecular engineering of two acceptors with the same core and side chains for increasing their mutual miscibility but different degrees of conjugation for broadening the light absorption allowed the formation of binary acceptor alloys with disparite ratios, laying the foundation for the pursuit of OPVs with high values of
V
OC
, high PCEs, and high stabilities.
Binary acceptor alloys based on two A′′-D′A′D′-A′′ small molecule acceptors having the same core but different end groups provided OPV with high PCE,
V
oc
and stability.
This paper reports on the design, fabrication, and characterization of a new class of wideband liquid RF micro-electromechanical-system reflective and absorptive switches. A number of different ...liquids are considered, including mercury, Galinstan, and ultrapure and ionic water. We first briefly review the performance of liquid-metal switches made by mercury and Galinstan. Such switches demonstrate excellent off-state insertion loss of less than 1.3 dB up to 100 GHz (the loss includes a 1500-mum-long line) and on-state isolation of better than 20 dB from 20 to 100 GHz. The main part of this paper, however, focuses on significantly transforming these designs to actually absorb and not reflect the incident power in their on-state, while at the same time maintaining their excellent off-state performance. Absorptive behavior is particularly important for high-power applications. Simpler materials such as water are proven to be very effective for wideband absorptive switches. In particular, three classes of water-based absorptive switches are discussed depending on the level of the signal coupling to water. At 10-40 GHz, the optimal design exhibits off-state insertion loss of less than 1.3 dB, on-and off-state return loss of less than 10 dB, and on-state isolation of 27.5-dB isolation at 40 GHz.
This study presents the synthesis of small-molecule acceptors having the structure A-D-A′-D-A-where A, A′, and D represent the end group, the core and π-bridge unit, respectively-that form the active ...layers with the polymer PM6 for organic photovoltaics. Increasing the number of core perylenetetracarboxylic diimide (PDI) units and conjugating them with thienothiophene (TT) or dithiophenepyrrole (DTP) π-bridge units enhanced the intramolecular charge transfer (ICT) and also increased effective conjugation, thereby, improving the light absorption and molecular packing. The absorption coefficient of hPDI-DTP-IC2F (two PDI with DTP) has the highest value (8 × 10
4
cm
−1
) because it featured the greatest degree of ICT, being much larger than that of PDI-TT-IC2F (one PDI with TT), hPDI-TT-IC2F (two PDI with TT) and PDI-DTP-IC2F (one PDI with DTP) (1.64 × 10
4
cm
−1
). The PM6:hPDI-DTP-IC2F device provided the highest power conversion efficiency (PCE) of 11.6%; this value was more than twice that of the PM6:PDI-DTP-IC2F (4.8%) device. This large increase in the PCE of the devices from the one-PDI core to two-PDI core case can be attributed to the two-PDI core case having (i) a stronger ICT, (ii) proper molecular packing that provided higher and more balanced carrier mobilities and (iii) a smaller energy loss than for the one-PDI case. Therefore, increasing the number of PDI units that were conjugated with suitable chromophores for stronger ICT in small molecule acceptors can be an effective way for enhancing the efficiency of organic photovoltaics.
This study presents the synthesis of small-molecule acceptors having the structure A-D-A′-D-A-where A, A′, and D represent the end group, the core and π-bridge unit, respectively-that form the active layers with the polymer PM6 for organic photovoltaics.
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