Concomitant development of 6,6-phenyl-C61-butyric acid methyl ester (PCBM) aggregation and poly(3-hexylthiophene) (P3HT) crystallization in bulk heterojunction (BHJ) thin-film (ca. 85 nm) solar cells ...has been revealed using simultaneous grazing-incidence small-/wide-angle X-ray scattering (GISAXS/GIWAXS). With enhanced time and spatial resolutions (5 s/frame; minimum q ≈ 0.004 Å–1), synchrotron GISAXS has captured in detail the fast growth in size of PCBM aggregates from 7 to 18 nm within 100 s of annealing at 150 °C. Simultaneously observed is the enhanced crystallization of P3HT into lamellae oriented mainly perpendicular but also parallel to the substrate. An Avrami analysis of the observed structural evolution indicates that the faster PCBM aggregation follows a diffusion-controlled growth process (confined by P3HT segmental motion), whereas the slower development of crystalline P3HT nanograins is characterized by constant nucleation rate (determined by the degree of supercooling and PCBM demixing). These two competing kinetics result in local phase separation with space-filling PCBM and P3HT nanodomains less than 20 nm in size when annealing temperature is kept below 180 °C. Accompanying the morphological development is the synchronized increase in electron and hole mobilities of the BHJ thin-film solar cells, revealing the sensitivity of the carrier transport of the device on the structural features of PCBM and P3HT nanodomains. Optimized structural parameters, including the aggregate size and mean spacing of the PCBM aggregates, are quantitatively correlated to the device performance; a comprehensive network structure of the optimized BHJ thin film is presented.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Organic semiconductors’ inherent flexibility makes them appealing for advanced applications such as wearable electronics, e‐skins, or pressure sensors, and can even be used to enhance their intrinsic ...electronic properties. Unfortunately, these applications for organic materials are currently hindered by the lack of a quantitative understanding of the interplay between their electrical and mechanical properties. In this work, this gap is filled by presenting an accurate methodology able to predict quantitatively the effects of external deformation on the charge transport properties of any organic semiconductors. Three prototypical materials are investigated, showing that the experimental variation of charge carrier mobility with strain is fully reproduced, even in a wide range of deformations applied along different crystal axes. The results indicate that the intrinsic electro‐mechanical response of the materials varies by orders of magnitude within the class of organic semiconductors, a difference rationalized observing that the mobility trend is primarily influenced by the transfer integrals’ variation, rather than by a modification of the crystal phonons. In light of its robustness, accuracy, and low computational cost, this protocol represents an ideal tool to quantify the electro‐mechanical response in new organic compounds, thus establishing a reliable route for a full exploitation of strain engineering in advanced technologies.
It is shown that it is possible to fully rationalize the relation between mechanical deformation and electronic properties of organic molecular semiconductors through a suitable and accessible theory, achieving quantitative agreement with experiments across orders‐of‐magnitude differences. The protocol provides the tools to identify rapidly new compounds sensitive/insensitive to mechanical deformation for advanced applications such as flexible and wearable devices, like e‐skins.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Substitution of the heteroatoms in the aromatic end‐groups of three diketopyrrolopyrrole containing small molecules is investigated to evaluate how such substitutions affect various physical ...properties, charge transport, and the performance in bulk heterojunction solar cells. While the optical absorption and frontier orbital energy levels are insensitive to heteroatom substitution, the materials' solubility, thermal properties, film morphology, charge carrier mobility, and photovoltaic performance are altered significantly. Differences in material properties are found to arise from changes in intra‐ and intermolecular interactions in the solid state caused by heteroatom substitution, as revealed by the single crystal structures of three compounds. This study demonstrates a systematic investigation of structure–property relationships in conjugated small molecules.
The effects of heteroatom substitutions on the functional properties of diketopyrrolopyrrole‐containing molecules are systematically investigated to identify the internal structure–property relationships. While the optical absorption and energy levels are insensitive to the heteroatom substitution, the materials' single crystal structures, capability of film formation, carrier mobility, and photovoltaic performance are significantly changed by the heteroatom substitutions.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Existing models for the electronic properties of conjugated polymers do not capture the spatial arrangement of the disordered macromolecular chains over which charge transport occurs. Here, we ...present an analytical and computational description in which the morphology of individual polymer chains is dictated by well-known statistical models and the electronic coupling between units is determined using Marcus theory. The multiscale transport of charges in these materials (high mobility at short length scales, low mobility at long length scales) is naturally described with our framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational variability and spatial correlation. Our model offers a predictive approach to connecting processing conditions with transport behavior.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Display omitted
•A series of BBBTs with different side chains were designed and synthesized.•The mobility properties of BBBTs film were evaluated in OFETs device.•The effect of side chains on the ...mobility properties were investigated by XRD and AFM.
A series of novel benzo2,1-b:3,4-b’bis1-benzothiophene (BBBT) derivatives with different side-chains were synthesized and characterized. And their mobility properties were evaluated based on their active layers in OFETs devices. By means of simple thermal annealing, the devices based on BBBT-4 and BBBT-6 exhibited typical p-type FETs behavior with average hole mobilities of 0.28 and 0.124 cm2 V−1 s−1, respectively. Furthermore, the structure-property relationships of these semiconductors were also investigated by XRD and AFM.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Impedance spectroscopy was used to investigate the charge transportation and accumulation mechanisms in a mixed-host emissive layer (EML) of phosphorescent organic light-emitting diodes (OLEDs). 1, ...3, 5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi) and 4, 4′, 4″-tris(N-carbazolyl)-triphenylamine (TCTA) materials were used as the electron transport and hole transport layers, respectively, to fabricate the mixed-host EML device. The results showed enhanced current and power efficiency owing to the use of the same material as the mixed-host EML, eliminating energy barriers within the device, coupled with the negative interfacial charges in the polarized TPBi material. The hole- and electron-split devices of the mixed-host EML OLED were analyzed to comprehensively understand the enhanced electrical properties within the device. Subsequently, the capacitance-frequency (C–F) characteristics of the devices were simulated with an equivalent circuit to quantitatively determine the capacitance and resistance in each organic layer at specific voltages (0–4 V) representing each characteristic step on the capacitance-voltage (C–V) curve.
Display omitted
•Impedance spectroscopy technique for characterizing mixed host EML PhOLED.•Enhanced current efficiency depends on the absence of an energy barrier and NIC in polarized TPBi.•The analyzed hole and electron split devices revealed the accumulation of charges in the dopant.•Simulation at specific voltages determined the capacitance of organic layers and trapped charges.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Developing nonchlorinated solvent-processed polymeric semiconductors to avoid environmental concerns and health hazards caused by chlorinated solvents is especially urgent. Here, a molecular design ...strategy, composed of backbone fluorination and side chain optimization, is used for preparing high-solubility and high-performance azaisoindigo-based polymers. The effects of different backbones and side chains on the solubility, film crystallinity, molecular stacking, and charge transport properties are mainly investigated. A long linear hybrid siloxane-based chain (C6-Si7) is chosen to improve the solubility, while the incorporation of fluorine (F) is used to enhance the film crystallinity and charge mobility. By optimizing the backbone and side chain, both solubility and charge mobility of the azaisoindigo-based polymer are significantly improved. As a result, PAIIDBFT-Si films processed with toluene, tetrahydrofuran, ether, and alkanes, achieved charge mobilities of 4.14, 3.78, 2.14, and 2.34 cm2 V–1 s–1, respectively. The current study provides an effective strategy for the design and synthesis of high-performance polymeric semiconductors processed with nonchlorinated solvents.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Conjugated polymer films are promising in wearable X-ray detection. However, achieving optimal film microstructure possessing good electrical and detection performance under large deformation via ...scalable printing remains challenging. Herein, we report bar-coated high-performance stretchable films based on a conjugated polymer P(TDPP-Se) and elastomer SEBS blend by optimizing the solution-processing conditions. The moderate preaggregation in solution and prolonged growth dynamics from a solvent mixture with limited dissolving capacity is critical to forming aligned P(TDPP-Se) chains/crystalline nanofibers in the SEBS phase with enhanced π–π stacking for charge transport and stress dissipation. The film shows a large elongation at break of >400% and high mobilities of 5.29 cm2 V–1 s–1 at 0% strain and 1.66 cm2 V–1 s–1 over 500 stretch–release cycles at 50% strain, enabling good X-ray imaging with a high sensitivity of 1501.52 μC Gyair –1 cm–2. Our work provides a morphology control strategy toward high-performance conjugated polymer film-based stretchable electronics.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
A wide range of nanophotonic applications rely on polarization‐dependent plasmonic resonances, which usually requires metallic nanostructures that have anisotropic shape. This work demonstrates ...polarization‐dependent plasmonic resonances instead by breaking symmetry via material permittivity. The study shows that molecular alignment of a conducting polymer can lead to a material with polarization‐dependent plasma frequency and corresponding in‐plane hyperbolic permittivity region. This result is not expected based only on anisotropic charge mobility but implies that also the effective mass of the charge carriers becomes anisotropic upon polymer alignment. This unique feature is used to demonstrate circularly symmetric nanoantennas that provide different plasmonic resonances parallel and perpendicular to the alignment direction. The nanoantennas are further tuneable via the redox state of the polymer. Importantly, polymer alignment could blueshift the plasma wavelength and resonances by several hundreds of nanometers, forming a novel approach toward reaching the ultimate goal of redox‐tunable conducting polymer nanoantennas for visible light.
Traditional anisotropic nanoantennas have asymmetric shape. In this work, symmetry is instead broken by straining of a conducting polymer, leading to an in‐plane anisotropic plasma frequency. This enables circularly symmetric nanoantennas with polarization‐dependent localized surface plasmon resonances. The polarization dependence is consistent with inverse changes of the effective mass and mobility of thecharge carriers along different in‐plane directions.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A grand challenge in materials science is to identify the impact of molecular composition and structure across a range of length scales on macroscopic properties. We demonstrate a unified ...experimental-theoretical framework that coordinates experimental measurements of mesoscale structure with molecular-level physical modeling to bridge multiple scales of physical behavior. Here we apply this framework to understand charge transport in a semiconducting polymer. Spatially-resolved nanodiffraction in a transmission electron microscope is combined with a self-consistent framework of the polymer chain statistics to yield a detailed picture of the polymer microstructure ranging from the molecular to device relevant scale. Using these data as inputs for charge transport calculations, the combined multiscale approach highlights the underrepresented role of defects in existing transport models. Short-range transport is shown to be more chaotic than is often pictured, with the drift velocity accounting for a small portion of overall charge motion. Local transport is sensitive to the alignment and geometry of polymer chains. At longer length scales, large domains and gradual grain boundaries funnel charges preferentially to certain regions, creating inhomogeneous charge distributions. While alignment generally improves mobility, these funneling effects negatively impact mobility. The microstructure is modified in silico to explore possible design rules, showing chain stiffness and alignment to be beneficial while local homogeneity has no positive effect. This combined approach creates a flexible and extensible pipeline for analyzing multiscale functional properties and a general strategy for extending the accesible length scales of experimental and theoretical probes by harnessing their combined strengths.
PDF
