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The true structure of alternating conjugated polymers—the state‐of‐the‐art materials for many organic electronics—often deviates from the idealized picture. Homocoupling defects are in fact inherent to the widely used cross‐coupling polymerization methods. Nevertheless, many polymers still perform excellently in the envisaged applications, which raises the question if one should really care about these imperfections. This article looks at the relevance of chemical precision (and lack thereof) in conjugated polymers covering the entire spectrum from the molecular scale, to the micro and mesostructure, up to the device level. The different types of polymerization errors for the alkoxylated variant of the benchmark (semi)crystalline polymer poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (PBTTT) are identified, visualized, and quantified and a general strategy to avoid homocoupling is introduced. Through a combination of experiments and supported by simulations, it is shown that these coupling defects hinder fullerene intercalation and limit device performance as compared to the homocoupling‐free analog. This clearly demonstrates that structural defects do matter and should be generally avoided, in particular when the geometrical regularity of the polymer is essential. These insights likely go beyond the specific PBTTT derivatives studied here and are of general relevance for the wider organic electronics field. [ABSTRACT FROM AUTHOR]

Doping plays a critical role in organic electronics, and dopant design has been central in the development of functional and stable doping. In this study, there is departure from conventional molecular dopants and a new class of dopants are reported – aromatic ionic dopants (AIDs). AIDs consist of a pair of aromatic cation and anion that are responsible for molecular doping reaction and charge balancing separately. It is shown that the first AID made from cycloheptatrienyl (tropylium) cation and pentacyanocyclopentadienide anion (PCCp), abbreviated as T‐PCCp, can function as an effective p‐type dopant to dope polydioxythiophenes. Here, tropylium cation induces the doping reaction while the PCCp anion stabilizes the generated polarons and bipolarons. With T‐PCCp, a highly doped (≈120 S/cm) and stable system is achieved up to 150 °C, an orthogonal (sequential)solution processing resulting from the immiscibility of the dopant and the polymer host, and a high‐resolution direct micropatterning with laser writing resulted from a thermally activated doping process. [ABSTRACT FROM AUTHOR]

Degradable organic semiconductors have significant potential for transient and biomedical organic electronics, but there have been only a few studies on fully degradable conjugated polymers (CPs) that achieve high electrical performance. In addition, these examples are limited to p‐type CPs. In this study, a series of fully degradable n‐type CPs, naphthalene diimide (NDI)‐based terpolymer (PNDIT2/IM‐f) are developed. The incorporation of an imine linker (IM) into the CP backbone affords the capability of facile hydrolysis degradation while maintaining efficient π‐conjugations and excellent electrical properties. An additional benefit of this molecular design is the systematic tunability of the degradation characteristics and electrical performance depending on the IM content (fIM). At the optimal point (fIM = 0.45) that enables complete degradation of the polymer under acidic conditions, the resulting PNDIT2/IM‐0.45 film exhibits high electron mobility (μe) of 0.04 cm2 V−1 s−1 in organic field‐effect transistors (OFETs), demonstrating excellent potential as transient OFETs. The high μe value is mainly attributed to the enlarged edge‐on orientations and tighter stacking of PNDIT2/IM‐f crystallites as increasing fIM. Thus, this study provides useful guidelines for the design of fully degradable n‐type CPs and establishes an important correlation between the molecular structure−electronic performance−transient properties. [ABSTRACT FROM AUTHOR]

Conjugated microporous polymers (CMPs) are a unique class of porous materials that have an integrated π‐conjugated system and permanent intrinsic porosity. They are of great interest because of their outstanding performance in gas sorption, photoredox catalysis, energy storage, organic light‐emitting diodes (OLEDs), and sensing applications. However, conventional chemically synthesized CMPs are solid powders and have poor solubility, which makes it difficult to process and integrate devices, and has become a bottleneck preventing their practical applications. Electropolymerization (EP) is a simple and efficient method for the preparation of CMP films, which simultaneously completes material synthesis and film processing. More importantly, the microstructure of the CMP films can be effectively controlled by electrochemical parameters. In this review, first, the basic synthetic principles and strategies of CMP films via EP are introduced, allowing for facile optimization of the structure and properties. Then, the recent progress of the EP CMP films is focused upon in organic electronics, energy storage, sensors, chemical capture and separation, and electrocatalysts. Finally, the challenges and outlook for EP CMP films are addressed. [ABSTRACT FROM AUTHOR]

The past few decades have witnessed the tremendous development of semiconducting polymers in electronic applications, which is inextricably related to the diversity of polymer structure. The change of polymer structure significantly influences the polymer packing, thin film morphology, and other optoelectronic properties, thus meeting the need for different device applications. With the development of synthetic chemistry and theoretical computation, many high‐performance building blocks and polymers have emerged. Among them, isoindigo‐ and isoindigo derivatives‐based polymers are widely studied in various fields of organic electronics, and many of them showed excellent properties. This review summarizes the synthetic tactics of isoindigo‐derived monomers and polymers. Moreover, the structural modification strategies of polymers are discussed in detail, including the modification of isoindigo derivatives and the regulation of polymer type. Using isoindigo‐derived polymers, various applications, such as organic field‐effect transistors, chemical sensors, organic electrochemical transistors, organic phototransistors, organic photovoltaics, organic thermoelectrics, organic spin valves, and biophotonic applications, are introduced to illustrate the important effects of structural modification. [ABSTRACT FROM AUTHOR]

A comprehensive investigation of four polydiketopyrrolopyrroles (PDPPs) with increasing ethylene glycol (EG) content and varying nature of comonomer is presented, and guidelines for the design of efficient mixed ion‐electron conductors (MIECs) are deduced. The studies in NaCl electrolyte‐gated organic electrochemical transistors (OECTs) reveal that a high amount of EG on the DPP moiety is essential for MIEC. The PDPP containing 52 wt% EG exhibits a high volumetric capacitance of 338 F cm−3 (at 0.8 V), a high hole mobility in aqueous medium (0.13 cm2 V−1 s−1), and a μC* product of 45 F cm−1 V−1 s−1. OECTs using this polymer retain 97% of the initial drain‐current after 1200 cycles (90 min of continuous operation). In a cell growth medium, the OECT‐performance is fully maintained as in the NaCl electrolyte. In vitro cytotoxicity and cell viability assays reveal the excellent cell compatibility of these novel systems, showing no toxicity after 24 h of culture. Due to the excellent OECT performance with a considerable cycling stability for 1200 cycles and an outstanding cell compatibility, these PDPPs render themselves viable for in vitro and in vivo bioelectronics. [ABSTRACT FROM AUTHOR]

Ionic‐electronic coupling across the entire volume of conjugated polymer films endows organic electrochemical transistors (OECTs) with high transconductance (gm) and low operating voltage. However, OECTs utilize liquid electrolytes, which limit their long‐term operation, reproducibility, and integration while solid electrolytes typically result in inefficient ion transport. Here, a solid polymer electrolyte is shown that can facilitate good electrochemical response in conjugated polymers and yield high OECT performance. This allows for the OECT‐based pressure sensors, modulated through a pressure sensitive ionic doping process. The pressure sensor exhibits the highest sensitivity ever measured (≈10 000 kPa−1) and excellent stability. Flexible sensor arrays achieve static capture of spatial pressure distribution and enable monitoring of dynamic pressure stimuli. The findings here demonstrate that all‐solid‐state OECTs are good candidates for providing rich tactile information, enabling applications for soft robotics, health monitoring, and human‐machine interfaces. [ABSTRACT FROM AUTHOR]

Elucidating the interrelation between the molecular structure and charge transport properties in conjugated polymer thin films is an essential issue in developing the design principle of high‐performance polymer materials for application in organic electronics. In particular, the backbone planarity is suggested to be a key element that governs the transport performance, especially in recently developed donor–acceptor (D–A)‐type copolymers exhibiting high mobility, whereas the direct evaluation of the intrinsic transport performance, usually realized only within the small crystalline domains, is difficult by using conventional macroscopic measurements. Here, it is demonstrated that a D–A type copolymer, PDPPF‐DTT, which consists of furan‐flanked diketopyrrolopyrrole (DPP) and dithienothiophene (DTT) units in the conjugated backbone, exhibits a highly efficient charge transport performance within the crystalline domains with a remarkably low activation energy of less than 8 meV, based on microscopic measurements using field‐induced electron spin resonance spectroscopy. This high transport performance is primarily caused by the high backbone planarity realized by introducing furan‐flanked DPP and fused dithienothiophene units, which is demonstrated from the density functional theory calculations. This result provides a microscopic indication of the effectiveness of the present molecular design to produce a planar backbone and realize highly efficient charge transport performance. [ABSTRACT FROM AUTHOR]

Recently, 2D monolayer films of conjugated polymers have gained increasing attention owing to the preeminence of 2D inorganic films that exhibit unique optoelectronic and mechanical properties compared to their bulk analogs. Despite numerous efforts, crystallization of semiconducting polymers into highly ordered 2D monolayer films still remains challenging. Herein, a dynamic‐template‐assisted meniscus‐guided coating is utilized to fabricate continuous, highly ordered 2D monolayer films of conjugated polymers over a centimeter scale with enhanced backbone π–π stacking. In contrast, monolayer films printed on solid substrates confer upon the 1D fiber networks strong alkyl side‐chain stacking at the expense of backbone packing. From single‐layers to multilayers, the polymer π‐stacks change from edge‐on to bimodal orientation as the film thickness reaches ≈20 nm. Spectroscopic and cyclic voltammetry analysis reveals an abrupt increase in J‐aggregation and absorption coefficient and a decrease in bandgap and highest occupied molecular orbital level until critical thickness, possibly arising from the straightened polymer backbone. This is corroborated by an abrupt increase in hole mobility with film thickness, reaching a maximum of 0.7 cm2 V−1 s−1 near the critical thickness. Finally, fabrication of chemical sensors incorporating polymer films of various thicknesses is demonstrated, and an ultrahigh sensitivity of the ≈7 nm thick ultrathin film (bilayers) to 1 ppb ammonia is shown. [ABSTRACT FROM AUTHOR]

The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) into poly(3-hexylthiophene-2,5-diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X-ray data suggest that F4TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π-stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6-8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F4TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm2 V−1 s−1 in the most crystalline P3HT samples. Temperature-dependent conductivity measurements show that polaron mobility in SqP-doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature. [ABSTRACT FROM AUTHOR]

A general method is proposed to produce oriented and highly crystalline conducting polymer layers. It combines the controlled orientation/crystallization of polymer films by high-temperature rubbing with a soft-doping method based on spin-coating a solution of dopants in an orthogonal solvent. Doping rubbed films of regioregular poly(3-alkylthiophene)s and poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2- b]thiophene) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) yields highly oriented conducting polymer films that display polarized UV-visible-near-infrared (NIR) absorption, anisotropy in charge transport, and thermoelectric properties. Transmission electron microscopy and polarized UV-vis-NIR spectroscopy help understand and clarify the structure of the films and the doping mechanism. F4TCNQ− anions are incorporated into the layers of side chains and orient with their long molecular axis perpendicular to the polymer chains. The ordering of dopant molecules depends closely on the length and packing of the alkyl side chains. Increasing the dopant concentration results in a continuous variation of unit cell parameters of the doped phase. The high orientation results in anisotropic charge conductivity (σ) and thermoelectric properties that are both enhanced in the direction of the polymer chains (σ = 22 ± 5 S cm−1 and S = 60 ± 2 µV K−1). The method of fabrication of such highly oriented conducting polymer films is versatile and is applicable to a large palette of semiconducting polymers. [ABSTRACT FROM AUTHOR]

Over the years, solution-processable conjugated oligomers and polymers have proven to be very promising for application in organic electronic devices. In addition to tuning the chemical structure of the materials, the role of morphology has been identified as a key parameter in determining device performance. Conjugated polymers are typically semicrystalline in nature consisting of both crystalline and amorphous domains giving rise to a wealth of superstructures. In comparison to classical non-conjugated semicrystalline polymers, they bear the additional advantage of absorbing light. This makes UV-vis absorption spectroscopy an excellent tool to monitor polymer aggregation and crystallization in-situ both in solution and in films. With this feature article we point out the delicate interplay between solution processing and the obtained morphology in polythiophenes and low bandgap copolymers. Subtle changes in the preparation protocol lead to significant changes in textures and also give rise to polymorphism. Solvent vapor annealing and solution crystallization are highlighted as tools to control the nucleation and growth processes in semicrystalline polymer films. Structure-function relationships between morphological, optical and electronic properties are demonstrated. [ABSTRACT FROM AUTHOR]

The detailed characterization of a dialkoxyphenylene-difluorobenzothiadiazole based conjugated polymer poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) is reported. PPDT2FBT closely tracks theoretical photocurrent production while maintaining a high fill factor in remarkably thick films. In order to understand the properties that enable PPDT2FBT to function with thick active layers, the effect of film thickness on the material properties and device parameters was carefully studied and compared to three benchmark polymers. Optical modeling, grazing incidence wide angle X-ray scattering, cross-sectional transmission electron microscopy, transient photoconductivity, and extensive device work were carried out and have clarified the key structural features and properties that allow such thick active layers to function efficiently. The unique behavior of thick PPDT2FBT films arises from high vertical carrier mobility, an isotropic morphology with strong, vertical π-π stacking, and a suitable energy band structure. These physical characteristics allow efficient photocurrent extraction, internal quantum efficiencies near 100% and power conversion efficiencies over 9% from exceptionally thick active layers in both conventional and inverted architectures. The ability of PPDT2FBT to function efficiently in thick cells allows devices to fully attenuate incident sunlight while providing a pathway to defect-free film processing over large areas, constituting a major advancement toward commercially viable organic solar cells. [ABSTRACT FROM AUTHOR]

Optoelectronic properties, supramolecular assemblies, and morphology variation of polymeric semiconductors are governed by six fundamental chemical features. These features are molecular weight, bond length alternation (BLA), planarity, aromatic resonance energy, substituents, and intermolecular interactions. O f these features the specific role of B LA in determining the performance of a polymeric semiconductor in practical technological applications is so far unknown. This study investigates this question and reports the novel finding that the optoelectronic, microscopic (supramolecular packing), and macroscopic (morphology variation and device performance) properties of model semiconducting polymers depend on the conjugated polymer backbone enlargement, which is directly related to the BLA. Extensive studies are performed in both single-component polymer films and their blends with fullerene derivatives. Understanding the specific structure-properties relations will lead to significant advancement in the area of organic electronics, since it will set new design rules toward further optimization of polymer chemical structures to enhance the device performances. [ABSTRACT FROM AUTHOR]

The effects of the incorporation of semiconducting single-walled nanotubes (sc-SWNTs) with high purity on the bulk heterojunction (BHJ) organic solar cell (OSC) based on regioregular poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (rr-P3HT:PCBM) are reported for the first time. The sc-SWNTs induce the organization of the polymer phase, which is evident from the increase in crystallite size, the red-shifted absorption characteristics and the enhanced hole mobility. By incorporating sc-SWNTs, OSC with a power conversion efficiency (PCE) as high as 4% can be achieved, which is ≈8% higher than our best control device. A novel application of sc-SWNTs in improving the thermal stability of BHJ OSCs is also demonstrated. After heating at 150 °C for 9 h, it is observed that the thermal stability of rr-P3HT:PCBM devices improves by more than fivefold with inclusion of sc-SWNTs. The thermal stability enhancement is attributed to a more suppressed phase separation, as shown by the remarkable decrease in the formation of sizeable crystals, which in turn can be the outcome of a more controlled crystallization of the blend materials on the nanotubes. [ABSTRACT FROM AUTHOR]

Spatial control of cell detachment is potentially of great interest when selecting cells for clonal expansion and in order to obtain a homogeneous starting population of cells aimed for tissue engineering purposes. Here, selective detachment and cell sorting of human primary keratinocytes and fibroblasts is achieved using thin films of a conjugated polymer. Upon electrochemical oxidation, the polymer film swells, cracks, and finally detaches taking cells cultured on top along with it. The polymer can be patterned using standard photolithography to fabricate a cross-point matrix with polymer pixels that can be individually addressed and thus detached. Detachment occurs above a well-defined threshold of +0.7 V versus Ag/AgCl, allowing the use of a relatively simple and easily manufactured passive matrix-addressing configuration, based on a resistor network, to control the cell-sorting device. [ABSTRACT FROM AUTHOR]

Nanostructured oxide arrays have received significant attention as charge injection and collection electrodes in numerous optoelectronic devices. Zinc oxide (ZnO) nanorods have received particular interest owing to the ease of fabrication using scalable, solution processes with a high degree of control of rod dimension and density. Here, vertical ZnO nanorods as electron injection layers in organic light emitting diodes are implemented for display and lighting purposes. Implementing nanorods into devices with an emissive polymer, poly(9,9-dioctyluorene-alt-benzothiadiazole) (F8BT) and poly(9,9-di- n-octylfluorene-alt- N-(4-butylphenyl)dipheny-lamine) (TFB) as an electron blocking layer, brightness and efficiencies up to 8602 cd m−2 and 1.66 cd A−1 are achieved. Simple solution processing methodologies combined with postdeposition thermal processing are highlighted to achieve complete wetting of the nanorod arrays with the emissive polymer. The introduction of TFB to minimize charge leakage and nonradiative exciton decay results in dramatic increases to device yields and provides an insight into the operating mechanism of these devices. It is demonstrated that the detected emission originates from within the polymer layers with no evidence of ZnO band edge or defect emission. The work represents a significant development for the ongoing implementation of ZnO nanorod arrays into efficient light emitting devices. [ABSTRACT FROM AUTHOR]

Organic electronic semiconducting materials exhibit complex atomic structures with a lack of periodicity that lead to charge carrier localization which, in turn, strongly affects the electronic transport properties of these materials. To understand charge carrier localization and electronic transport in organic semiconductors, simulations that take into account the details of the atomic structure of the material are of utmost importance. In this article, computational methods that can be used to simulate the electronic properties of organic semiconductors are reviewed and an overview of the results that have been obtained from such simulations is given. Using these methods the effects of static disorder, thermal disorder and interfaces between domains are investigated and the microscopic origin of these effects is identified. It is shown that in strongly disordered conjugated polymer materials the main origin of the localization of charge carrier wave functions is the disordered long-range electrostatic potential. In ordered polymers, thermal disorder of main chains leads to wave function localization. In small molecule based organic semiconductors, grain boundaries introduce localized trap states at the points where electronic coupling is the strongest. It is also demonstrated that detailed atomistic simulations are necessary for quantitative and sometimes even qualitative description of charge mobility in organic materials. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of solar cells based on a conjugated polymer (donor) and a fullerene derivative (acceptor) is very sensitive to the morphology of the active layer. One detrimental feature, which is often encountered in non-optimal morphologies, is the occurrence of fullerene blobs in a finely mixed matrix containing both donor and acceptor material. Here, the effects of such fullerene blobs are studied in detail with a three-dimensional drift-diffusion model. It includes the effects of exciton diffusion and quenching; space-charge; recombination, generation, drift and diffusion of charge carriers; and the injection/extraction of carriers at the contacts. The influence of blob size and shape, and matrix composition are quantified. The latter has the strongest effect on the overall efficiency, as most of the current is transported through the mixed phase. The total current flowing out of the solar cell can be split up in a part which comes from the interfacial region between the acceptor phase and the mixed phase, and a part that stems from the mixed phase itself. Depending on the bias voltage and the morphology, one or the other contribution is dominant. Finally, it is shown how both contributions can be computed with a simple one-dimensional drift-diffusion simulator. [ABSTRACT FROM AUTHOR]

Bulk heterojunction (BHJ) organic solar cells are fabricated with the polymer semiconductor aligned in the plane of the film to probe charge recombination losses associated with aggregates characterized by varying degrees of local order. 100% uniaxial strain is applied on ductile poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) BHJ films and characterize the resulting morphology with ultraviolet-visible absorption spectroscopy and grazing incidence X-ray diffraction. It is found that the strained films result in strong alignment of the highly ordered polymer aggregates. Polymer aggregates with lower order and amorphous regions also align but with a much broader orientation distribution. The solar cells are then tested under linearly polarized light where the light is selectively absorbed by the appropriately oriented polymer, while maintaining a common local environment for the sweep out of photogenerated charge carriers. Results show that charge collection losses associated with a disordered BHJ film are circumvented, and the internal quantum efficiency is independent of P3HT local aggregate order near the heterojunction interface. Uniquely, this experimental approach allows for selective excitation of distinct morphological features of a conjugated polymer within a single BHJ film, providing insight into the morphological origin of recombination losses. [ABSTRACT FROM AUTHOR]

Self-assembly of conjugated organic semiconductors into ordered, larger scale entities is a critical process to achieve efficient charge transport at the nano- through macro-scales, and various methodologies aimed at enhancing molecular ordering have been introduced. However, mechanistic understanding is limited. Here, a mechanistic elucidation of poly(3-hexylthiophene) (P3HT) molecular self-assembly is proposed based on experimental demonstration of controlled, solution-based P3HT self-assembly into rod-like polycrystalline nanostructures. The synergistic combination of nonsolvent addition and ultrasonication facilitates rod-like P3HT nanostructure formation in solution. Importantly, through sequential application of both treatments, nanostructure length can be easily modulated, and the assembly process is shown to follow a simple 2-step crystallization model, which depends upon nucleation followed by growth. Through arrays of experimental results, the validity of 2-step crystallization is confirmed and is proposed as a comprehensive platform to understand self-assembly processes of conjugated polymers into larger, ordered mesoscale entities. [ABSTRACT FROM AUTHOR]

Current organic semiconductors for organic photovoltaics (OPV) have relative dielectric constants (relative permittivities, εr) in the range of 2-4. As a consequence, Coulombically bound electron-hole pairs (excitons) are produced upon absorption of light, giving rise to limited power conversion efficiencies. We introduce a strategy to enhance εr of well-known donors and acceptors without breaking conjugation, degrading charge carrier mobility or altering the transport gap. The ability of ethylene glycol (EG) repeating units to rapidly reorient their dipoles with the charge redistributions in the environment was proven via density functional theory (DFT) calculations. Fullerene derivatives functionalized with triethylene glycol side chains were studied for the enhancement of εr together with poly( p-phenylene vinylene) and diketopyrrolopyrrole based polymers functionalized with similar side chains. The polymers showed a doubling of εr with respect to their reference polymers in identical backbone. Fullerene derivatives presented enhancements up to 6 compared with phenyl-C61-butyric acid methyl ester (PCBM) as the reference. Importantly, the applied modifications did not affect the mobility of electrons and holes and provided excellent solubility in common organic solvents. [ABSTRACT FROM AUTHOR]

For the purpose of investigating the effect of fluorination position on D−A type conjugated polymer on photophysical and photovoltaic properties, two types of fluorinated polymere are synthesized, HF with fluorination on electron-donating unit and FH with fluorination on electron-accepting unit. Compared to non-fluorinated polymer, fluorinated polymers exhibit deeper HOMO energy levels without change of bandgap and stronger vibronic shoulder in UV−visible absorption, indicating that fluorination enhances intermolecular interaction. HF with fluorinated D unit exhibits well-developed fibril network, low bimolecular recombination and high hole mobility, which lead a high PCE of 7.10% in conventional single-junction solar cells, which is higher than the PCE (6.41%) of FH with fluorinated A unit. Therefore, this result demonstrates that fluorination on electron-donating unit in D−A polymers could be a promising strategy for achieving high performance polymer solar cells. [ABSTRACT FROM AUTHOR]

Nanoscale hybrid dielectrics composed of an ultra-thin polymeric low-κ bottom layer and an ultra-thin high-κ oxide top layer, with high dielectric strength and capacitances up to 0.25 μFcm−2, compatible with low-voltage, low-power, organic electronic circuits are demonstrated. An efficient and reliable fabrication process, with 100% yield achieved on lab-scale arrays, is demonstrated by means of pulsed laser deposition (PLD) for the fast growth of the oxide layer. With this strategy, high capacitance top gate (TG), n-type and p-type organic field effect transistors (OFETs) with high mobility, low leakage currents, and low subthreshold slopes are realized and employed in complementary-like inverters, exhibiting ideal switching for supply voltages as low as 2 V. Importantly, the hybrid double-layer allows for a neat decoupling between the need for a high capacitance, guaranteed by the nanoscale thickness of the double layer, and for an optimized semiconductor-dielectric interface, a crucial point in enabling high mobility OFETs, thanks to the low-κ polymeric dielectric layer in direct contact with the polymer semiconductor. It is shown that such decoupling can be achieved already with a polymer dielectric as thin as 10 nm when the top oxide is deposited by PLD. This paves the way for a very versatile implementation of the proposed approach for the scaling of the operating voltages of TG OFETs with very low level of dielectric leakage currents to the fabrication of low-voltage organic electronics with drastically reduced power consumption. [ABSTRACT FROM AUTHOR]

A synergistic approach combining new material design and interfacial engineering of devices is adopted to produce high efficiency inverted solar cells. Two new polymers, based on an indacenodithieno[3,2- b]thiophene-difluorobenzothiadiazole (PIDTT-DFBT) donor-acceptor (D-A) polymer, are produced by incorporating either an alkyl thiophene (PIDTT-DFBT-T) or alkyl thieno[3,2-b]thiophene (PIDTT-DFBT-TT) π-bridge as spacer. Although the PIDTT-DFBT-TT polymer exhibits decreased absorption at longer wavelengths and increased absorption at higher energy wavelengths, it shows higher power conversion efficiencies in devices. In contrast, the thiophene bridged PIDTT-DFBT-T shows a similar change in its absorption spectrum, but its low molecular weight leads to reduced hole mobilities and performance in photovoltaic cells. Inverted solar cells based on PIDTT-DFBT-TT are explored by modifying the electron-transporting ZnO layer with a fullerene self-assembled monolayer and the MoO3 hole-transporting layer with graphene oxide. This leads to power conversion efficiencies as high as 7.3% in inverted cells. PIDTT-DFBT-TT's characteristic strong short wavelength absorption and high efficiency suggests it is a good candidate as a wide band gap material for tandem solar cells. [ABSTRACT FROM AUTHOR]

Naphthalenediimide (NDI)-based polymers co-polymerized with thienyl units are an interesting class of polymer semiconductors because of their good electron mobilities and unique film microstructure. Despite these properties, understanding how the extension of the thienyl co-monomer affects charge transport properties remains unclear. With this goal in mind, we have synthesized a series of NDI derivatives of the parent poly{[ N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene) (P(NDI2OD-T2)), which exhibited excellent electron mobility. The strategy comprises both the extension of the donor o-conjugation length and the heteroatomic fusion of the thiophene rings. These newly synthesized compounds are characterized experimentally and theoretically vis-à-vis with P(NDI2OD-T2) as the reference. UV-vis data and cyclic-voltammetry are adopted to assess the effect of the donor modification on the frontier energy levels and on the bandgap. Intra-molecular polaronic effects are accounted for by computing the internal reorganization energy with density functional theory (DFT) calculations. Finally electrons and holes transport is experimentally investigated in field-effect transistors (FETs), by measuring current-voltage characteristics at variable temperatures. Overall we have identified a regime where inter-molecular effects, such as the wavefunction overlap and the degree of energetic disorder, induced by the different donor group prevail over polaronic effects and are the leading factors in determining electrons mobility. [ABSTRACT FROM AUTHOR]

To devise a reliable strategy for achieving specific HOMO and LUMO energy level modulation via alternating donor-acceptor monomer units, we investigate a series of conjugated polymers (CPs) in which the electron withdrawing power of the acceptor group is varied, while maintaining the same donor group and the same conjugated chain conformation. Through experiment and DFT calculations, good correlation is identified between the withdrawing strength of the acceptor group, the HOMO and LUMO levels, and the degree of orbital localization, which allows reliable design principles for CPs. Increasing the acceptor strength results in an enhanced charge transfer upon combination with a donor monomer and a more pronounced decrease of the LUMO level. Moreover, while HOMO states remain delocalized along the polymer chain, LUMO states are strongly localized at specific bonds within the acceptor group. The degree of LUMO localization increases with increasing polymer length, which results in a further drop of the LUMO level and converges to its final value when the number of repeat units reaches the characteristic conjugation length. Based on these insights we designed PBT8PT, which exhibits 6.78% power conversion efficiency after device optimization via the additive assisted annealing, demonstrating the effectiveness of our predictive design approach. [ABSTRACT FROM AUTHOR]

To achieve the full potential of scalable and cost‐effective organic electronic devices, developments are being made in both academic and industry environments to move toward continuous solution‐processing techniques that make use of safe and environmentally benign "green" solvents. In this work, the first example of a transistor device that is fully solution processed using only green solvents is demonstrated. This achievement is enabled through a novel multistage cleavable side chain process that provides aqueous solubility for semiconducting conjugated polymers, paired with aqueous inkjet printing of PEDOT:PSS electrodes, and a solution deposited ion gel electrolyte as the dielectric layer. The resulting organic electrochemical transistor devices operate in accumulation mode and reach maximum transconductance values of 1.1 mS at a gate voltage of − 1 V. Normalizing the transconductance value to the channel dimensions yields gm/W = 2200 S m−1 (µC* = 22 F cm−1 V−1 s−1), making these devices suitable for a range of applications requiring small signal amplification such as transistors, biosensors, and ion pumps. This new material design and device process paves the way toward scalable, safe, and efficient production of organic electronic devices. [ABSTRACT FROM AUTHOR]

To better understand the correlation of the dielectric properties with the photovoltaic response in conjugated polymer:fullerene bulk heterojunction materials, the concept of introducing minimal structural change is employed to increase the polymer dielectric constant via polar cyano groups added to the end of butyl or octyl side chains in the poly(dithienosilole‐thienopyrrolodione) system. Density functional theory calculations confirm that the polar groups do not affect the polymer electronic structure but can lead to an increase in overall dipole moment depending on the polymer chain conformation. Despite the increased dielectric constant (from 2.7 to 4.3 for cyano‐octyl side chains and from 2.7 to 3.2 for the cyano‐butyl analogues), the device characteristics employing the cyano‐containing polymers are inferior to those of the devices made with unfunctionalized alkyl chains. It is found that the hole mobilities for the cyano‐containing polymers are two orders of magnitude lower compared to those for the parent polymers and suggest this is due to an increase in energetic disorder caused by the strong local permanent dipoles associated with the cyano groups. The study highlights the complexity in the relationship between the dielectric constant of organic materials, the morphologies that are induced, and their photovoltaic performance. Introducing polar cyano groups to the end of dithienosilole‐thienopyrrolodione polymer side chains leads to an increase in polymer dielectric constant, without significantly affecting the optical gaps and energy levels. However, this structural modification results in inferior device parameters and ultimately lower power conversion efficiencies, because of the drastic decrease in hole mobilities which is caused by higher energetic disorders. [ABSTRACT FROM AUTHOR]