Porous Nanostructured Composite Film for Visible-to-Infrared Camouflage with Thermal Management

Progressive advancement in modern detection technologies entails multispectral compatible camouflage. Previously, infrared camouflage materials, such as photonic crystals and metamaterials, have been developed, but improved multispectral compatibility, easy fabrication, and cost-effectiveness remain a challenge. Here, we report a nanostructured composite film based on oxalate-rich porous alumina (OPA) for visible-to-infrared compatible camouflage and simultaneous thermal management. The nanostructured composite film consists of a visible-transparent OPA layer, a composite layer of OPA/metal oxides, and an aluminum substrate. Each functional layer exhibits desirable reflection/emission properties for infrared and visible camouflage. Infrared camouflage is realized by the high reflection (low emission) of the metal substrate in both infrared-detected bands (3–5 and 8–14 μm). Meanwhile, radiative cooling arising from the intrinsic absorption of oxalate in the undetected band (5–8 μm) enhances surface heat dissipation. In addition, background-matching colors can be tuned by the metal oxides in the composite layer for visible camouflage, such as green for forest and brown for desert. This work provides a facile strategy to modulate multispectral absorption/emission properties with much flexibility and thus has great potential for energy conversion and stealth applications

Incorporating a Nonfused Electron Acceptor into Double-Cable Conjugated Polymers for Single-Component Organic Solar Cells with a Photo Response up to 900 nm

The manipulation of end groups in near-infrared (NIR) acceptors incorporated in double-cable conjugated polymers plays a pivotal role in governing the film morphology and charge transport properties in single-component organic solar cells (SCOSCs). In this study, we employ a NIR-photoresponse acceptor, comprising para-substituted benzene and 4H-cyclopenta­[1,2-b:5,4-b′]­dithiophene (CPDT) as the core and 2-(3-oxo-2,3-dihydroinden-1ylidene)­malononitrile (IC) as the end group, into the double-cable conjugated polymers. By varying the degree of fluorination on the end group, we systematically tuned the optical and electronic characteristics of these materials. Three different double-cable polymers, namely, PF-0 (without fluorination), PF-2 (with two fluorine atoms), and PF-4 (with four fluorine atoms), are successfully applied in SCOSCs. Remarkably, the PF-4-based SCOSC exhibits an impressive power conversion efficiency of 7.60%, accompanied by a high photocurrent of 18.56 mA/cm2 and broad photoresponse spanning from 300 to 900 nm. The observed enhanced performance is attributed to the increased crystallinity and improved charge transport properties in PF-4. This study sheds light on the crucial role of end-group engineering in advancing the development of efficient SCOSCs

Enhancing the Performance of Small-Molecule Organic Solar Cells via Fused-Ring Design

Organic solar cells (OSCs) as the promising green energy technology have drawn much attention in the last two decades. In comparison to polymer solar cells, small-molecule organic solar cells (SMOSCs) have the advantages of precise chemical structure and molecular weight, purification feasibility, batch reproducibility, etc. Despite of the recent advances in molecular design, the efficiencies of SMOSCs are still lagging behind those of polymer-based OSCs. In this work, a new small-molecule donor (SMD) with a fused-ring-connected bridge denoted F-MD has been designed and synthesized. When F-MD was applied into SMOSCs, the F-MD:N3 blends exhibited a power conversion efficiency (PCE) of over 13%, which is much higher than that of the linear π-bridged molecule L-MD based devices (8.12%). Further studies revealed that the fused-ring design promoted the planarity of the molecular conformation and facilitated charge transport in OSCs. More importantly, this strategy also lowered the crystallinity and self-aggregation of the films, and hence optimized the microstructure and phase separation in the corresponding blends. Thereby, the F-MD-based blends have been evidenced to have better exciton dissociation and reduced charge recombination in comparison with the L-MD counterparts, explaining the enhanced PCEs. Our work demonstrates that the fused-ring π-bridge strategy in small-molecule-donor design is an effective pathway to promote the efficiency of SMOSCs as well as enhance the diversity of SMD materials

Length Effect of Alkyl Linkers on the Crystalline Transition in Naphthalene Diimide-Based Double-Cable Conjugated Polymers

The alkyl chains as linkers in double-cable conjugated polymers play an important role in the solubility, packing motif, morphology, and voltage loss in single-component organic solar cells (SCOSCs). In this work, we incorporate alkyl linkers with lengths from hexyl (C6H12) to hexadecyl (C16H32) into naphthalene diimide-based double-cable conjugated polymers. These polymers show a parabolic-type distribution in crystallinity, in which the crystalline degree of the polymers is enhanced in sequence from P06 (C6H12 linker) to P12 (C12H24 linker) and then decreased in longer alkyl linkers. These differences bring into deviations like optical bandgaps, packing motif, charge transport, and photovoltaic performance in SCOSCs. This work demonstrates the importance of linkers’ length on crystallinity and packing motif as well as provides a new viewpoint in guiding the design of new double-cable conjugated polymers

Double-Cable Conjugated Polymers with Rigid Phenyl Linkers for Single-Component Organic Solar Cells

Nonradiative recombination loss is the key factor to be responsible for low open-circuit voltage (Voc) in organic solar cells (OSCs), which can be reduced via tuning the chemical structure of conjugated materials. However, the intrinsic correlation between them was rarely studied. In this work, we were able to build a strong connection between chemical structure and nonradiative recombination loss, which was then used to lower the voltage losses in OSCs. The studies start from designing several double-cable conjugated polymers with rigid phenyl linkers, which guarantee the precise distance between donor (D) backbone and acceptor (A) side units. In addition, the number of phenyl linkers was changed from one to three, so as to provide different D/A distances. The universal studies of solar cells, morphology, and voltage losses showed that longer D/A distance provided lower nonradiative recombination losses and hence higher Voc in single-component OSCs. Our results demonstrate that extending the D/A distance via rigid phenyl linkers is an efficient way to reduce the voltage losses in OSCs

Modulating the Central Units of Polymerized Nonfused Electron Acceptors for All-Polymer Solar Cells

Polymerized small-molecule acceptors (PSMAs) based on nonfused-core structures have obtained much attention in the domain of all-polymer solar cells (all-PSCs) due to simplified synthetic complexity. In this work, two nonfused PSMAs, namely, P1 and P2, with similar molecular backbones but with the central units featuring two alkoxy side chains with varied substitution positions have been designed and synthesized. In P1, two alkyloxy side units locate at the two sides of the benzene core, while in P2, they locate on the same side. All-PSCs are fabricated by utilizing PBDB-T as the donor, followed by the investigation of their device performance. The P2-based all-PSCs yield a power conversion efficiency of 9.33% with a robust short-circuit current (JSC) of 16.93 mA/cm2 due to favorable active-layer morphology. Herein, it is demonstrated that optimizing the central unit is conducive to the development of high-performance polymer acceptors, which are essential for manufacturing low-cost and efficient all-PSCs

Miscibility-Controlled Mechanical and Photovoltaic Properties in Double-Cable Conjugated Polymer/Insulating Polymer Composites

Flexibility is one of the main characteristics of organic solar cells (OSCs), which enables them to possess potential applications in flexible electronics. The study of flexibility (such as mechanical and bending behaviors) of the photoactive layers and the strategy to enhance the flexibility are important research topics in this field. In this work, we have focused on studying the flexibility of a single photoactive layer via using a double-cable conjugated polymer instead of two-component bulk-heterojunction layers. This simplified system enabled us to add the insulating polymers into the double-cable polymer to generate a polymer/polymer mixtures. The results found that the miscibility between the double-cable conjugated polymer and insulating polymers was the key factor to influence the mechanical and photovoltaic properties. Good miscibility by using polystyrene as an additive can provide better crack-onset strains as well as high efficiency, while lower miscibility by using polydimethylsiloxane as an additive exhibited low efficiencies in single-component OSCs

Incorporating Naphthalene and Halogen into Near-Infrared Double-Cable Conjugated Polymers for Single-Component Organic Solar Cells with Low-Voltage Losses

The invention of near-infrared pedant-based double-cable conjugated polymers has demonstrated remarkable efficacy in single-component organic solar cells (SCOSCs). This work focuses on the innovative double-cable conjugated polymers aimed at attaining good absorption and suitable energy levels. Specifically, in the aromatic side units, the electron-donating (D) part is designed using a thieno[3,4-c]pyrrole-4,6-dione (TPD) as a core unit, flanked by two cyclopentadithiophene groups on either side. The electron-deficient (A) terminal groups consist of 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene) malononitrile (NC), which can be further modified through fluorination to modulate the physical properties and packing modes of the acceptor material. The resulting double-cable conjugated polymers exhibit broad absorption spectra spanning 500–850 nm and possess lowered Frontier energy levels when incorporating fluorine elements, providing decreased voltage losses in SCOSCs. Therefore, SCOSCs fabricated using these polymers have demonstrated power conversion efficiencies ranging from 7.6 to 10.2%, in which fluorine-containing double-cable conjugated polymers showed higher PCEs due to more favorable crystalline packing, enhanced exciton dissociation probability, and charge-transporting ability

Dimerized Nonfused Electron Acceptor Based on a Thieno[3,4‑<i>c</i>]pyrrole-4,6-dione Core for Organic Solar Cells

In this work, the first dimerized nonfused electron acceptor (NFEA), based on thieno­[3,4-c]­pyrrole-4,6-dione as the core, has been designed and synthesized. The dimerized acceptor and its single counterpart exhibit similar energy levels but different absorption spectra due to their distinct aggregation behavior. The dimerized acceptor-based organic solar cells (OSCs) demonstrate a higher power conversion efficiency of 11.05%, accompanied by enhanced thermal stability. This improvement is attributed to the enhancement of the short-circuit current density and fill factor, along with an increase in the glass transition temperature. Characterizations of exciton dynamics and film morphology reveal that a dimerized acceptor-based device possesses an enhanced exciton dissociation efficiency and a well-established charge transport pathway, explaining its improved photovoltaic performance. All these results indicate that the dimerized NFEA as a promising candidate can achieve efficiency–stability–cost balance in OSCs

Miscibility-Controlled Mechanical and Photovoltaic Properties in Double-Cable Conjugated Polymer/Insulating Polymer Composites

Flexibility is one of the main characteristics of organic solar cells (OSCs), which enables them to possess potential applications in flexible electronics. The study of flexibility (such as mechanical and bending behaviors) of the photoactive layers and the strategy to enhance the flexibility are important research topics in this field. In this work, we have focused on studying the flexibility of a single photoactive layer via using a double-cable conjugated polymer instead of two-component bulk-heterojunction layers. This simplified system enabled us to add the insulating polymers into the double-cable polymer to generate a polymer/polymer mixtures. The results found that the miscibility between the double-cable conjugated polymer and insulating polymers was the key factor to influence the mechanical and photovoltaic properties. Good miscibility by using polystyrene as an additive can provide better crack-onset strains as well as high efficiency, while lower miscibility by using polydimethylsiloxane as an additive exhibited low efficiencies in single-component OSCs