In the past few decades, novel syntheses of a wide range of nanoparticles (NPs) with well‐defined chemical composition and structure have opened tremendous opportunities in areas ranging from optical ...and electronic devices to biomedical markers. Controlling the assembly of such well‐defined NPs is important to effectively harness their unique properties. The assembly of NPs at liquid–liquid interfaces is becoming a central topic both in surface and colloid science. Hierarchical structures, including 2D films, 3D capsules, and structured liquids, have been generating significant interest and are showing promise for physical, chemical, and biological applications. Here, a brief overview of the development of the self‐assembly of NPs at liquid–liquid interfaces is provided, from theory to experiment, from synthetic NPs to bio‐nanoparticles, from water–oil to water–water, and from “liquid‐like” to “solid‐like” assemblies.
Self‐assembly of nanoparticles (NPs) at liquid–liquid interfaces opens new pathways for nanotechnology through the controlled fabrication of nanoscopic materials with unique optical, magnetic, and electronic properties. A brief overview of recent developments in this field is provided, from theory to experiment, from synthetic NPs to bio‐nanoparticles, from water–oil to water–water, and from “liquid‐like” to “solid‐like” assemblies.
Over the past 30 years, atomic force microscopy (AFM) has played an important role in elucidating the structure and properties of polymer surfaces. AFM-based techniques have enabled the quantitative ...determination of the physicochemical properties of polymer surfaces with high spatial resolution and under a wide variety of conditions. Coupled with the improvements in spatial and temporal resolution, multiparametric and multifunctional characterization has revealed the delicate interplay between structure, dynamics, and properties at the surfaces of complex systems. Here we summarize some of the significant advances that have been made in synthetic polymeric materials, most in the past 10 years, where AFM has been crucial, and we provide our perspective on where AFM will be insightful in future and instrumental in advancing emerging areas.
Nanoparticles assemble at the interface between two fluids into disordered, liquid-like arrays where the nanoparticles can diffuse laterally at the interface. Using nanoparticles dispersed in water ...and amine end-capped polymers in oil, nanoparticle surfactants are generated in situ at the interface overcoming the inherent weak forces governing the interfacial adsorption of nanoparticles. When the shape of the liquid domain is deformed by an external field, the surface area increases and more nanoparticles adsorb to the interface. Upon releasing the field, the interfacial area decreases, jamming the nanoparticle surfactants and arresting further shape change. The jammed nanoparticles remain disordered and liquid-like, enabling multiple, consecutive deformation and jamming events. Further stabilization is realized by replacing monofunctional ligands with difunctional versions that cross-link the assemblies. The ability to generate and stabilize liquids with a prescribed shape poses opportunities for reactive liquid systems, packaging, delivery, and storage.
Polymeric materials, used predominantly in their bulk form, are now finding increasing application as thin films or where the end-use dimensions are approaching the size of the individual polymer ...molecules. This introduces questions concerning the perturbations to the fundamental static and dynamic properties arising when the pervaded volume of the polymer must conform to the finite size limitations. These properties include the single chain dimensions, entanglement molecular weight, anisotropy of polymer molecules, and wetting. For block copolymers, where the disparity in the chemical nature of the constituent blocks gives rise to microphase-separated morphologies, confinement can introduce fundamental changes in the ordering transitions of the copolymer, changes in the fundamental length scales and morphologies typically seen in the bulk, and changes in the orientation of the microdomains. As the size scale decreases, the surface-to-volume ratio increases, and as such, interfacial interactions and surface energies become increasingly important. The dramatic density at a surface and preferential interactions at surfaces and interfaces can have a profound impact on the chain dynamics and in multicomponent systems and block copolymers the preferential segregations of one component to the surface or interface. While the orientation of morphologies relative to the interface will occur, the extent to which surface effects propagate into the film and the adhesion of one material to another are important to understand for end-use applications. For interfaces between disparate materials, as for example between an organic polymer and a metal, transport of electrons or holes from one medium to the next, where there is a disparity in the work function, reduces to the behavior and nature of the polymer immediately at the interface. Here we summarize some of the significant advances that have been made on polymer thin films and interfaces, where the polymer chains can be squeezed, and provide some insight into future and emerging areas in the field.
Inspired by the remarkable promotion of power conversion efficiency (PCE), commercial applications of organic photovoltaics (OPVs) can be foreseen in near future. One of the most promising ...applications is semitransparent (ST) solar cells that can be utilized in value‐added applications such as energy‐harvesting windows. However, the single‐junction STOPVs utilizing fullerene acceptors show relatively low PCEs of 4%–6% due to the limited sunlight absorption because it is a dilemma that more photons need to be harvested in UV–vis–near‐infrared (NIR) region to generate high photocurrent, which leads to the significant reduction of device transparency. This study describes the development of a new small‐bandgap electron‐acceptor material ATT‐2, which shows a strong NIR absorption between 600 and 940 nm with an Egopt of 1.32 eV. By combining with PTB7‐Th, the as‐cast OPVs yield PCEs of up to 9.58% with a fill factor of 0.63, an open‐circuit voltage of 0.73 V, and a very high short‐circuit current of 20.75 mA cm−2. Owing to the favorable complementary absorption of low‐bangap PTB7‐Th and small‐bandgap ATT‐2 in NIR region, the proof‐of‐concept STOPVs show the highest PCE of 7.7% so far reported for single‐junction STOPVs with a high transparency of 37%.
A small‐bandgap electron acceptor, ATT‐2, is designed and synthesized. By combining PTB7‐Th donor, the power conversion efficiencies reach 9.58% and 7.74% for opaque and semitransparent devices, respectively. The highest PCE among single‐junction STOPVs can be attributed to the beneficial complementary near‐infrared absorption of the low‐bandgap donor and small‐bandgap acceptor. Non‐fullerene acceptors are thus very promising for the development of high‐performance STOPVs.
The chemical structure of donors and acceptors limit the power conversion efficiencies achievable with active layers of binary donor-acceptor mixtures. Here, using quaternary blends, double cascading ...energy level alignment in bulk heterojunction organic photovoltaic active layers are realized, enabling efficient carrier splitting and transport. Numerous avenues to optimize light absorption, carrier transport, and charge-transfer state energy levels are opened by the chemical constitution of the components. Record-breaking PCEs of 18.07% are achieved where, by electronic structure and morphology optimization, simultaneous improvements of the open-circuit voltage, short-circuit current and fill factor occur. The donor and acceptor chemical structures afford control over electronic structure and charge-transfer state energy levels, enabling manipulation of hole-transfer rates, carrier transport, and non-radiative recombination losses.
The unidirectional extension of a smaller fused-ring system into a larger one in a single direction will increase the conjugation length, allowing a fine-tuning of electronic properties. Here, we ...designed and synthesized a unidirectionally extended fused-8-ring-based nonfullerene acceptor, AOIC, and a bidirectionally extended fused-11-ring electron acceptor, IUIC2, and compared these with the parent fused-5-ring electron acceptor, F5IC. They share the same electron-accepting groups and alkylphenyl side chains but have different fused-ring electron-donating units. Core extension from 5 to 11 rings up-shifts the energy levels, red shifts the absorption spectra, and reduces bandgaps. The unidirectionally extended AOIC has the highest mobility (2.1 × 10–3 cm2 V–1 s–1) relative to the parent F5IC (1.0 × 10–3 cm2 V–1 s–1) and the bidirectionally extended IUIC2 (4.7 × 10–4 cm2 V–1 s–1). Upon blending with the donor PTB7-Th, AOIC-based organic photovoltaic cells show an efficiency of 13.7%, much better than that of F5IC-based cells (5.61%) and IUIC2-based cells (4.48%).
Self‐doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3‐dibromopropane (NDI‐NI) or trans‐1,4‐dibromo‐2‐butene (NDI‐CI) via quaternization ...polymerization. These NDI‐based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene‐based, non‐fullerene‐based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI‐NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI‐CI, affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function (WF) of air‐stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.
Electronically active ionenes were realized by integration of naphthalene diimide into a polymer backbone. These conductive polymers have a low degree of crystalline order, show a great processing advantage to remove energy barriers between organic semiconductors and metal electrodes, and afford fullerene‐based, non‐fullerene‐based, as well as ternary organic solar cells with high performance and a maximum efficiency of 16.9 %.
Free-standing nanorod arrays of poly(3-hexylthiophene) (P3HT) were fabricated on indium tin oxide/glass substrates using anodic aluminum oxide (AAO) templates. The AAO templates were treated with a ...low molecular weight polydimethylsiloxane mold-release agent to reduce their surface energy of the template and interactions with the P3HT. Using a thermal nanoimprinting process, the templates were easily removed, generating nanorods on the surfaces of P3HT thin films. These unique structures were investigated for application in organic photovoltaic devices.
By using a combination of wide-angle X-ray diffraction (WAXD), mass density, and 13C solid-state nuclear magnetic resonance (NMR) measurements, a quantification of the absolute degree of ...crystallinity in regioregular poly(3-hexylthiophene) (rr-P3HT) is presented. A regiorandom P3HT (rra-P3HT), lacking long-range order, was used to separate the crystalline contribution from the total scattering in WAXD, thus yielding degrees of crystallinity in the range of 47–56% at room temperature for three different rr-P3HTs. For the same rr-P3HT with identical processing history, NMR yields degrees of crystallinity that are consistently ∼10% greater than that obtained by WAXD, which can only be explained by ordered chain segments in the amorphous phase. NMR results also suggest that rra-P3HT contains weakly ordered chain segments, which likely contribute to an underestimation of degree of crystallinity when determined from mass density measurements, if rra-P3HT is used to approximate a fully amorphous P3HT. The results shown in this study provide direct proof of three different types of P3HT chain segments: crystallites (i.e., long-range ordered chain packing), amorphous phase (i.e., disordered chain packing), and short-range ordered chain packing embedded in the amorphous phase. The presence of the short-range ordered chain packing is particularly important when correlating the morphology to macroscopic charge transport properties in P3HT-based devices. In general, those locally ordered chain segments, though not constituting a distinct phase, are believed to be of critical importance in determining the transport characteristics of conjugated semiconducting polymers with or without a distinct crystalline phase present.
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