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Top-gate polymer field-effect transistors based on charge accumulation in bilayers of two semiconducting polymers have been realized. Holes were confined at the interface between poly(3-hexyl thiophene) (P3HT) and a series of semiconducting polymers with ionization potential higher than P3HT. In contrast to conventional devices based on semiconductor-dielectric interfaces the current was found to saturate at high gate voltages. The more pronounced the current saturation is, the lower the applied source-drain voltage. Generic drift-diffusion device simulations were performed to explain this behavior in terms of the competing processes of charge transport along and charge transfer across the bilayer interface. Our results indicate that in order to block the charge transfer across the heterojunction the offset between the ionization potential of the two polymers needs to be at least 1.0 eV. [ABSTRACT FROM AUTHOR]

This review is focused on understanding of the charge-transport physics of high-mobility organic semiconductors at a molecular level. We review recent high-mobility small-molecule and conjugated polymer materials with a focus on crystalline materials that have been able to exceed mobilities of 0.5-1 cm2/V s. We discuss some of the main, competing factors that govern charge transport in these materials and present theoretical approaches that have been developed to describe systems in which moderately strong intermolecular electronic interactions and strong electron-phonon interactions are present. Finally, we review recent experimental results that have aimed to address the important question of whether at room-temperature charge carriers in these high-mobility organic semiconductors are in fact simply extended Bloch electrons that undergo occasional scattering processes or are localized on individual molecules and move by hopping. [ABSTRACT FROM AUTHOR]

The mobility μ of solution-processed organic semiconductorshas improved markedly to room-temperature values of 1–5 cm2 V−1 s−1. In spite of their growing technological importance, the fundamental open question remains whether charges are localized onto individual molecules or exhibit extended-state band conduction like those in inorganic semiconductors. The high bulk mobility of 100 cm2 V−1 s−1 at 10 K of some molecular single crystals provides clear evidence that extended-state conduction is possible in van-der-Waals-bonded solids at low temperatures. However, the nature of conduction at room temperature with mobilities close to the Ioffe–Regel limit remains controversial. Here we investigate the origin of an apparent ‘band-like’, negative temperature coefficient of the mobility (dμ/dT<0) in spin-coated films of 6,13-bis(triisopropylsilylethynyl)-pentacene. We use optical spectroscopy of gate-induced charge carriers to show that, at low temperature and small lateral electric field, charges become localized onto individual molecules in shallow trap states, but that a moderate lateral electric field is able to detrap them resulting in highly nonlinear, low-temperature transport. The negative temperature coefficient of the mobility at high fields is not due to extended-state conduction but to localized transport limited by thermal lattice fluctuations. [ABSTRACT FROM AUTHOR]

Abstract: Most conjugated polymer field-effect transistors rely on charge accumulation between an organic semiconductor and a gate dielectric. Much less use has been made of devices based on heterojunctions between two semiconducting polymers. Here we have realized ambipolar polymer field-effect transistors based on bilayers of two polyfluorene-based semiconducting polymers, poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)diphenylamine) and poly(9,9-dioctylfluorene-alt-benzothiadiazole). We show that the energy offset between the lowest unoccupied molecular orbitals of the two polymers of 1–1.5eV is sufficient to confine electrons at the bi-layer interface for n-type operation. However, the transfer current–voltage characteristics exhibit an unusual plateau. This is shown to be due to hole charge trapping in donor-like states in the TFB layer during p-type operation. [Copyright &y& Elsevier]

Abstract: We have demonstrated top-gate polymer field-effect transistors (FETs) with ultra-thin (30–50nm), room-temperature crosslinkable polymer gate dielectrics based on blending an insulating base polymer such as poly(methyl methacrylate) with an organosilane crosslinking agent, 1,6-bis(trichlorosilyl)hexane. The top-gate polymer transistors with thin gate dielectrics were operated at gate voltages less than −8V with a relatively high dielectric breakdown strength (>3MV/cm) and a low leakage current (10–100nA/mm2 at 2MV/cm). The yield of thin gate dielectrics in top-gate polymer FETs is correlated with the roughness of underlying semiconducting polymer film. High mobilities of 0.1–0.2cm2/Vs and on and off state current ratios of 104 were achieved with the high performance semiconducting polymer, poly(2,5-bis(3-alkylthiophen-2yl)thieno[3,2-b]thiophene. [Copyright &y& Elsevier]

The article provides an overview on the working principles of organic field-effect transistors and describe how both hole and electron transport take place in these devices. The authors first introduce the basics of field-effect transistors and define the parameters affecting the performance of the device in general. They then demonstrate the prerequisites for fabricating n-channel transistors. Lastly, they discuss both unipolar and ambipolar light-emitting transistors.

Colloidal nanorods of inorganic semiconductors are of interest for a range of optoelectronic devices. The ability to self-assemble these materials into ordered arrays by solution-processing techniques is crucial for achieving adequate device performance. Here we show that uniform ZnO nanorod films with defined nanorod alignment can be solution-deposited over large areas by controlling the surface energy of the nanorods through the choice of suitable ligands and by the fluid flow direction during growth. ZnO nanorods with long carbon chain ligands exhibit a smaller surface free energy than those with short carbon chain ligands resulting in better in-plane alignment and large domain sizes up to dozens of micrometers in spin-coated films. A model is presented to rationalize the observed self-assembly behavior. It is based on the formation of a lyotropic liquid crystalline phase on the surface of the liquid film which is facilitated by enhanced segregation of nanorods with low surface tension to the surface. Alignment of the nanorods is controlled by radial and vertical liquid flows in the drying solution. The ability to control the orientation of the nanorods and to achieve large domain size results in significant device performance improvement. Field-effect transistors with mobilities of up to 1.2–1.4 cm²N·s are demonstrated in spin-coated, in-plane aligned ZnO nanorod films subject to postdeposition hydrothermal growth. [ABSTRACT FROM AUTHOR]

Presents research which demonstrated an all-polymer semiconductor integrated device. Feature of a field-effect transistor (FET) driving a polymer light-emitting diode (LED); Performance of the FET; Explanation for high mobility of the FET; Future all-polymer optoelectronic integrated circuits.

We have investigated the dependence of bias-stress induced degradation in organic field-effect transistors on the device configuration. We show that separation of contact and channel effects is essential for understanding bias-stress instabilities. In coplanar device configurations, an increase in source contact resistance during current flow is primarily responsible for a rapid device degradation. In contrast, in staggered device configurations, the significantly slower reduction in current is primarily due to charge trapping in the channel leading to an increase in threshold voltage, while the contacts themselves do not exhibit significant degradation. [ABSTRACT FROM AUTHOR]

The effects of x-ray irradiation on the electrical performance of organic thin film transistors (OTFTs) have been examined up to equivalent lifetime doses for medical digital x-ray imaging backplanes. Transistor performance metrics have been assessed before and after exposures up to 500 Gy for bottom-gate, bottom-contact OTFTs of p-channel polytriarylamine and polyfluorene semiconductors. There is no discernible degradation in device performance for either material and no indication of the creation of additional trap states. In situ measurements indicate that x-ray exposure tends to reverse undesirable shifts in the threshold voltage due to prolonged atmospheric exposure and bias stress. [ABSTRACT FROM AUTHOR]

Charge modulation microscopy (CMM) is an electro-optical method that is capable of mapping the spatial distribution of induced charges in an organic field-effect transistor (OFET). Here, we report a new (and simple) implementation of CMM in transmission geometry with camera-based imaging. A significant improvement in data acquisition speed (by at least an order of magnitude) has been achieved while preserving the spatial and spectral resolution. To demonstrate the capability of the system, we measured the spatial distribution of the induced charges in an OFET with a polymer blend of indacenodithiophene-co-benzothiadiazole and poly-vinylcarbazole that shows micrometer-scale phase separation. We were able to resolve spatial variations in the accumulated charge density on a length scale of 500 nm. We demonstrated through a careful spectral analysis that the measured signal is a genuine charge accumulation signal that is not dominated by optical artifacts. [ABSTRACT FROM AUTHOR]

Ternary chalcogenides have emerged as potential candidates for ultrathin photovoltaics, and NaBiS2 nanocrystals (NCs) have gained appeal because of their months‐long phase‐stability in air, high absorption coefficients >105 cm−1, and a pseudo‐direct bandgap of 1.4 eV. However, previous investigations into NaBiS2 NCs used long‐chain organic ligands separating individual NCs during synthesis, which severely limits macroscopic charge‐carrier transport. In this work, these long‐chain ligands are exchanged for short iodide‐based ligands, allowing to understand the macroscopic charge‐carrier transport properties of NaBiS2 and evaluate its photovoltaic potential in more depth. It is found that ligand exchange results in simultaneous improvements in intra‐NC (microscopic) and inter‐NC (macroscopic) mobilities, while charge‐carrier localization still takes place, which places a fundamental limit on the transport lengths achievable. Despite this limitation, the high absorption coefficients enable ultrathin (55 nm thick) solar absorbers to be used in photovoltaic devices, which have peak external quantum efficiencies > 50%. In addition, temperature‐dependent transient current measurements uncover a small activation energy barrier of 88 meV for ion migration, which accounts for the strongly hysteretic behavior of NaBiS2 photovoltaic devices. This work not only reveals how the charge‐carrier transport properties of NaBiS2 NCs over several length and time scales are influenced by ligand engineering, but also unveils the facile ionic transport in this material, which limits the potential of NaBiS2 in photovoltaics. On the other hand, the discovery shows that there are opportunities to use this material in memristors, electrolytes, and other applications requiring ionic conduction. [ABSTRACT FROM AUTHOR]

Heterostructures of two‐dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two‐dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route. [ABSTRACT FROM AUTHOR]

Heterostructures of two‐dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two‐dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route. [ABSTRACT FROM AUTHOR]

Examines the misfit dislocations in epitaxial CoSi[sub 2]/Si (111) layers by scanning tunneling microscopy (STM). Observation on vertical atomic displacement; Determination of film thickness on STM topographs; Assessment on the strain heteroepitaxial layers.

Understanding the electronic structure of organic-organic heterointerfaces is crucial for many device applications of organic semiconductors. Here we have developed a simple analytical model to describe the effect of static dipolar disorder in a polymer dielectric on the density of states of an adjacent organic semiconductor. The degree of energetic disorder varies strongly with distance from the interface. Using a simple mobility model, we have been able to explain quantitatively both the magnitude as well as the gate voltage dependence of the field-effect mobility for polymer gate dielectrics with different dielectric constants. [ABSTRACT FROM AUTHOR]

Self-aligned printing is a recently developed bottom-up printing technique which utilizes the unique droplet motion on heterogeneous surfaces to define sub-100-nm critical features and surpasses the resolution which can commonly be achieved by direct printing by two orders of magnitude. Here we extend this method, which was originally implemented with conductive polymer inks, to fabrication of functional conductive nanostructures with gold nanoparticle ink. We also designed a configuration where the ink was printed between two lithographically defined patterns to facilitate the study of the channel formation. Channel lengths from 4 μm down to 60 nm were achieved by controlling the surface tension and drying time of the ink. A fluid dynamical model is presented to explain the mechanism by which the channel forms in the self-aligned printing technique. Field-effect transistors fabricated using gold self-aligned printed source-drain electrodes exhibit significantly improved output currents than those using conducting polymers. Unambiguous evidence for the submicrometer channel dimension is obtained by imaging the potential drop along the channel using scanning Kelvin probe microscopy. [ABSTRACT FROM AUTHOR]

n-Type organic electrochemical transistors (OECTs) and organic field-effect transistors (OFETs) are less developed than their p-type counterparts. Herein, polynaphthalenediimide (PNDI)-based copolymers bearing novel fluorinated selenophene-vinylene-selenophene (FSVS) units as efficient materials for both n-type OECTs and n-type OFETs are reported. The PNDI polymers with oligo(ethylene glycol) (EG7) side chains P(NDIEG7-FSVS), affords a high µC* of > 0.2 F cm-1 V-1 s-1, outperforming the benchmark n-type Pg4NDI-T2 and Pg4NDI-gT2 by two orders of magnitude. The deep-lying LUMO of-4.63 eV endows P(NDIEG7-FSVS) with an ultra-low threshold voltage of 0.16 V. Moreover, the conjugated polymer with octyldodecyl (OD) side chains P(NDIOD-FSVS) exhibits a surprisingly low energetic disorder with an Urbach energy of 36 meV and an ultra-low activation energy of 39 meV, resulting in high electron mobility of up to 0.32 cm² V-1 s-1 in n-type OFETs. These results demonstrate the great potential for simultaneously achieving a lower LUMO and a tighter intermolecular packing for the next-generation efficient n-type organic electronics. [ABSTRACT FROM AUTHOR]

Organic semiconductors with distinct molecular properties and large carrier mobilities are constantly developed in attempt to produce highly‐efficient electronic materials. Recently, designer molecules with unique structural modifications have been expressly developed to suppress molecular motions in the solid state that arise from low‐energy phonon modes, which uniquely limit carrier mobilities through electron–phonon coupling. However, such low‐frequency vibrational dynamics often involve complex molecular dynamics, making comprehension of the underlying electronic origins of electron–phonon coupling difficult. In this study, first a mode‐resolved picture of electron–phonon coupling in a series of materials that are specifically designed to suppress detrimental vibrational effects, is generated. From this foundation, a method is developed based on the crystalline orbital Hamiltonian population (COHP) analyses to resolve the origins—down to the single atomic‐orbital scale—of surprisingly large electron–phonon coupling constants of particular vibrations, explicitly detailing the manner in which the intermolecular wavefunction overlap is perturbed. Overall, this approach provides a comprehensive explanation into the unexpected effects of less‐commonly studied molecular vibrations, revealing new aspects of molecular design that should be considered for creating improved organic semiconducting materials. [ABSTRACT FROM AUTHOR]

Organic metal‐halide perovskites (OHPs) have recently attracted much attention as next‐generation semiconducting materials due to their outstanding opto‐electrical properties. However, OHPs currently suffer from the lack of efficient doping methods, while the traditional method of atomistic doping having clear limitations in the achievable doping range. While doping with molecular dopants, has been suggested as a solution to this problem, the action of these dopants is typically restricted to perovskite surfaces, therefore significantly reducing their doping potential. In this study, successful bulk inclusion of "magic blue", a molecular dopant, into 2D Ruddlesden–Popper perovskites is reported. This doping strategy of immersing the perovskite film in dopant solution increases the electrical current up to ≈60 times while maintaining clean film surface. A full mechanistic picture of such immersion doping is provided, in which the solvent molecule facilitates bulk diffusion of dopant molecule inside the organic spacer layer. Physical criteria for judicious choice of solvents in immersion doping are developed based on readily available solvent properties. The immersion doping method developed in this study that enables bulk molecular doping in OHPs will provide a strategic doping methodology for controlling electrical properties of OHPs for electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The article discusses research that has produced a polymer material that allows for n-type transistors that will allow for the production of printed complementary circuits that have a previously unrecognized rate of performance. This type of transistor, which is a semiconductor electronic switch utilized in any integrated circuit, utilizes organic molecules and polymers that can be processed from solution. This larger field is referred to as organic electronics. The polymer evaluated is highly soluble in organic solvents and is compatible with inkjet, flexographic and gravure printing.

The article "Theo Murphy International Scientific Meeting Between the UK and China on the Chemistry and Physics of Functional Materials" by Wenping Hu et al. is cited.

In an article published in Angewandte Chemie, Hiroshi Nishihara et al. present a new method for creating lateral heterojunctions in two-dimensional materials. These heterojunctions have rectifying properties and can be fabricated by immersing a coordination nanosheet made from zinc ions and benzenehexathiol into iron and copper salt solutions. This research has implications for utilizing the attractive properties of two-dimensional materials more effectively. The authors of the article include Choon Meng Tan, Naoya Fukui, Kenji Takada, Hiroaki Maeda, Ekaterina Selezneva, Cédric Bourgès, Hiroyasu Masunaga, Sono Sasaki, Kazuhito Tsukagoshi, Takao Mori, Henning Sirringhaus, and Hiroshi Nishihara. [Extracted from the article]

In an article published in Angewandte Chemie International Edition, Hiroshi Nishihara et al. present a new method for creating lateral heterojunctions in two-dimensional materials. These heterojunctions have rectifying properties and are formed by immersing a coordination nanosheet made from zinc ions and benzenehexathiol into iron and copper salt solutions. This research has implications for utilizing the attractive properties of two-dimensional materials more effectively. The authors of the article include Choon Meng Tan, Naoya Fukui, Kenji Takada, Hiroaki Maeda, Ekaterina Selezneva, Cédric Bourgès, Hiroyasu Masunaga, Sono Sasaki, Kazuhito Tsukagoshi, Takao Mori, Henning Sirringhaus, and Hiroshi Nishihara. [Extracted from the article]

• The structure of the first monolayer depends on the preparation process. • In case of spin coating the nucleation is mediated by edges of the monolayer. • For vapor deposition the nucleation is mediated by confinement with the substrate. • The mosaicity of the thin film crystals are determined by the nucleation process. The benzothieno-benzothiophene derivatives are among the best-performing organic semiconductor materials. Their triumphant application in electronic devices is correlated to their capability to form well-defined thin film structures featuring crystalline order at the substrate–organic interface. Thin films of the molecule 2,7-bis(2-(2-methoxy ethoxy)ethoxy) benzo[b]-benzo[4,5]thieno[2,3-d]thiophene (OEG-BTBT) are prepared by spin coating and physical vapor deposition using different experimental conditions. Atomically flat silicon oxide surfaces with defined surface energies are used as substrates. The crystalline morphology is studied for the monolayer regime up to thick films by X-ray reflectivity, grazing incidence X-ray diffraction and atomic force microscopy. Depending on the preparation process, substantial variations are found in the structure of the first monolayers. The highly flexible oligoethylene glycol side chains allow different monolayer formation processes. Also, the subsequent crystal growth strongly depends on the nucleation in the monolayer regime. Here, we observe two distinct nucleation scenarios, one directly at the substrate surface and one at the edges of sub-monolayer terraces. As a consequence, the mosaicity of the crystallites in thick films is strongly affected by the growth type. This work illustrates that different thin film preparation processes can result in different nucleation mechanisms for subsequent crystallization. Consequently, variations in the crystallographic order in device relevant films are observed. [ABSTRACT FROM AUTHOR]

Hybrid integration of n‐type oxide with p‐type polymer transistors is an attractive approach for realizing high performance complementary circuits on flexible substrates. However, the stability of solution‐processed oxide transistors is limiting the lifetime and reliability of such circuits. Oxygen vacancies are the main defect degrading metal oxide transistor performance when ambient oxygen adsorbs onto metal oxide films. Here, an effective surface passivation treatment based on negative oxygen ion exposure combined with UV light is demonstrated, that is able to significantly reduce surface oxygen vacancy concentration and improve the field effect mobility to values up to 41 cm2 V−1 s−1 with high on–off current ratio of 108. The treatment also reduces the threshold voltage shift after 2 days in air from 5 to 0.07 V. The improved stability of the oxide transistors also improves the lifetime of hybrid complementary circuits and stable operation of complementary, analog amplifiers is confirmed for 60 days in air. The suggested approach is facile and can be widely applicable for flexible electronics using low‐temperature solution‐processed metal oxide semiconductors. [ABSTRACT FROM AUTHOR]

Halide double perovskites have gained significant attention, owing to their composition of low‐toxicity elements, stability in air, and recent demonstrations of long charge‐carrier lifetimes that can exceed 1 µs. In particular, Cs2AgBiBr6 is the subject of many investigations in photovoltaic devices. However, the efficiencies of solar cells based on this double perovskite are still far from the theoretical efficiency limit of the material. Here, the role of grain size on the optoelectronic properties of Cs2AgBiBr6 thin films is investigated. It is shown through cathodoluminescence measurements that grain boundaries are the dominant nonradiative recombination sites. It also demonstrates through field‐effect transistor and temperature‐dependent transient current measurements that grain boundaries act as the main channels for ion transport. Interestingly, a positive correlation between carrier mobility and temperature is found, which resembles the hopping mechanism often seen in organic semiconductors. These findings explain the discrepancy between the long diffusion lengths >1 µm found in Cs2AgBiBr6 single crystals versus the limited performance achieved in their thin film counterparts. This work shows that mitigating the impact of grain boundaries will be critical for these double perovskite thin films to reach the performance achievable based on their intrinsic single‐crystal properties. [ABSTRACT FROM AUTHOR]

We report electroluminescence from ion-gel gated, field-effecttransistors based on the conjugated polymer, poly(9,9′-dioctylfluorene-co-benzothiadiazole)gated by an 1-ethyl-3-methylimidazoliumbis (trifluoromethylsulfonyl)imide/poly (styrene-block-ethylene oxide-block-styrene) ion gel, andinvestigate the mechanism for light emission. The devices emit lightfrom near the electron-injecting drain electrode when the drain sourcevoltage exceeds approximately the energy gap of the polymer (Vds> Eg/e). Charge accumulation spectroscopy is used to demonstratethe significantpenetration of the negative TFSI–ions into theF8BT assisted by the application of negative gate voltages, wherethey lead to significant p-type doping of the bulk of the F8BT film.In contrast, no evidence for diffusion of positive ions with positivegate voltages is observed, and this is consistent with the locationof the recombination zone in the proximity of electron injecting electrodeand the absence of a comparable electron current at positive gatevoltages. We conclude that in the light-emission regime the devicesoperate more akin to a hole-current dominated light-emitting electrochemicalcell than a transistor. [ABSTRACT FROM AUTHOR]

Organic semiconductors show efficient electroluminescence which has led to their commercialization in light-emitting diodes, but has also raised fundamental questions about their recombination and emission physics. Organic ambipolar field-effect transistors can support both hole and electron transport at the semiconductor–dielectric interface. Using their ability to emit light owing to charge recombination within the transistor channel should enable new ways to study the recombination physics and realize new electrooptical devices. Here we demonstrate ambipolar light-emitting transistors based on a semiconducting polymer with both efficient electron and hole transport and good photoluminescence efficiency. In our device configuration, electrons and holes injected from separate calcium and gold electrodes recombine radiatively within the channel. We can move the recombination zone with the applied gate and source–drain bias to any position within the channel. This provides a direct visualization and proof of coexisting electron and hole accumulation layers in an ambipolar transport regime. [ABSTRACT FROM AUTHOR]

We explore the charge transport properties of phytic acid (PA) doped polyaniline thin films prepared by the surfactant monolayer‐assisted interfacial synthesis (SMAIS). Structural and elemental analysis confirms the inclusion of PA in the thin films and reveals a progressive loss of crystallinity with the increase of PA doping content. Charge transport properties are interrogated by time‐resolved terahertz (THz) spectroscopy. Notably, independently of doping content and hence crystallinity, the frequency‐resolved complex conductivity spectra in the THz region can be properly described by the Drude model, demonstrating band‐like charge transport in the samples and state‐of‐the‐art charge carrier mobilities of ≈1 cm2V−1s−1. A temperature‐dependent analysis for the conductivity further supports band‐like charge transport and suggest that charge carrier mobility is primarily limited by impurity scattering. This work highlights the potential of PA doped polyaniline for organic electronics. [ABSTRACT FROM AUTHOR]

Organic thermoelectrics offer the potential to deliver flexible, low-cost devices that can directly convert heat to electricity. Previous studies have reported high conductivity and thermoelectric power factor in the conjugated polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). Here, we investigate the thermoelectric properties of PBTTT films in which the polymer chains were aligned uniaxially by mechanical rubbing, and the films were doped by a recently developed ion exchange technique that provides a choice over the counterions incorporated into the film, allowing for more optimized morphology and better stability than conventional charge transfer doping. To optimize the polymer alignment process, we took advantage of two Design of Experiment (DOE) techniques: regular two-level factorial design and central composite design. Rubbing temperature Trub and post-alignment annealing temperature Tanneal were the two factors that were most strongly correlated with conductivity. We were able to achieve high polymer alignment with a dichroic ratio >15 and high electrical conductivities of up to 4345 S/cm for transport parallel to the polymer chains, demonstrating that the ion exchange method can achieve conductivities comparable/higher than conventional charge transfer doping. While the conductivity of aligned films increased by a factor of 4 compared to unaligned films, the Seebeck coefficient (S) remained nearly unchanged. The combination of DOE methodology, high-temperature rubbing, and ion exchange doping provides a systematic, controllable strategy to tune structure–thermoelectric property relationships in semiconducting polymers. [ABSTRACT FROM AUTHOR]

The manufacture of high-performance, conjugated polymer transistor circuits on flexible plastic substrates requires patterning techniques that are capable of defining critical features with submicrometer resolution. We used solid-state embossing to produce polymer field-effect transistors with submicrometer critical features in planar and vertical configurations. Embossing is used for the controlled microcutting of vertical sidewalls into polymer multilayer structures without smearing. Vertical-channel polymer field-effect transistors on flexible poly(ethylene terephthalate) substrates were fabricated, in which the critical channel length of 0.7 to 0.9 micrometers was defined by the thickness of a spin-coated insulator layer. Gate electrodes were self-aligned to minimize overlap capacitance by inkjet printing that used the embossed grooves to define a surface-energy pattern. [ABSTRACT FROM AUTHOR]

The formidable rise of lead‐halide perovskite photovoltaics has energized the search for lead‐free perovskite‐inspired materials (PIMs) with related optoelectronic properties but free from toxicity limitations. The photovoltaic performance of PIMs closely depends on their defect tolerance. However, a comprehensive experimental characterization of their defect‐level parameters—concentration, energy depth, and capture cross‐section—has not been pursued to date, hindering the rational development of defect‐tolerant PIMs. While mainstream, capacitance‐based techniques for defect‐level characterization have sparked controversy in lead‐halide perovskite research, their use on PIMs is also problematic due to their typical near‐intrinsic character. This study demonstrates on four representative PIMs (Cs3Sb2I9, Rb3Sb2I9, BiOI, and AgBiI4) for which Photoinduced Current Transient Spectroscopy (PICTS) offers a facile, widely applicable route to the defect‐level characterization of PIMs embedded within solar cells. Going beyond the ambiguities of the current discussion of defect tolerance, a methodology is also presented to quantitatively assess the defect tolerance of PIMs in photovoltaics based on their experimental defect‐level parameters. Finally, PICTS applied to PIM photovoltaics is revealed to be ultimately sensitive to defect‐level concentrations <1 ppb. Therefore, this study provides a versatile platform for the defect‐level characterization of PIMs and related absorbers, which can catalyze the development of green, high‐performance photovoltaics. [ABSTRACT FROM AUTHOR]

The measurement of the mechanical properties of conjugated polymers can reveal highly relevant information linking optoelectronic properties to underlying microstructures and the knowledge of the glass transition temperature (Tg) is paramount for informing the choice of processing conditions and for interpreting the thermal stability of devices. In this work, we use dynamical mechanical analysis to determine the Tg of a range of state‐of‐the‐art conjugated polymers with different degrees of crystallinity that are widely studied for applications in organic field‐effect transistors. We compare our measured values for Tg to the theoretical value predicted by a recent work based on the concept of effective mobility ζ. The comparison shows that for conjugated polymers with a modest length of the monomer units, the Tg values agree well with theoretically predictions. However, for the near‐amorphous, indacenodithiophene–benzothiadiazole family of polymers with more extended backbone units, values for Tg appear to be significantly higher, predicted by theory. However, values for Tg are correlated with the sub‐bandgap optical absorption suggesting the possible role of the interchain short contacts within materials' amorphous domains. [ABSTRACT FROM AUTHOR]

Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy is an important tool for probing the structure of conjugated polymer films used in organic electronic devices. High-performance conjugated polymers are often donor-acceptor co-polymers which feature a repeat unit with multiple functional groups. To facilitate better application of NEXAFS spectroscopy to the study of such materials, improved understanding of the observed NEXAFS spectral features is required. In order to examine how the NEXAFS spectrum of a donor-acceptor co-polymer relates to the properties of the sub-units, a series of naphthalene diimide-thiophene-based co-polymers have been studied where the nature and length of the donor co-monomer has been systematically varied. The spectra of these materials are compared with that of a thiophene homopolymer and naphthalene diimide monomer enabling peak assignment and the influence of inter-unit electronic coupling to be assessed. We find that while it is possible to attribute peaks within the π* manifold as arising primarily due to the naphthalene diimide or thiophene sub-units, very similar dichroism of these peaks is observed indicating that it may not be possible to separately probe the molecular orientation of the separate sub-units with carbon K-edge NEXAFS spectroscopy. [ABSTRACT FROM AUTHOR]

We present a means to optically tune the emission of an organic laser reversibly over a range of 14 nm. This is enabled by incorporating a photochromic spiropyran (10,30-dihydro-10,30,30-trimethyl-6-nitrospiro[2H-1-benzopyran-2,20-(2H)-indole]) into the gain medium formed by the laser dye Rhodamine 700 in poly(methyl methacrylate). This is structured by nanoimprinting to form a distributed feedback resonator. Exposure of the device to ultraviolet and visible light leads to a reversible refractive index change of the photochromic additive and the gain medium, which enables the continuous shift of the laser wavelength. This is possible without compromising the optical gain properties of the device. [ABSTRACT FROM AUTHOR]

The effect of morphology and microstructure on the emission characteristics of ambipolar light-emitting field-effect transistors is studied using the polyfluorene copolymer F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)] as a model system. Different intensity distributions of the emission zones of amorphous, polycrystalline, and aligned F8BT films are demonstrated. Electroluminescence maps of the channel region are produced by overlaying a series of images recorded during gate voltage sweeps. They show a correlation to the microcrystalline structure of the F8BT and are assumed to visualize the current density distribution within the transistor channel. [ABSTRACT FROM AUTHOR]

The x-ray stability of photodiodes made of poly(9,9-di-n-octylfluorene-co-benzothiadiazole):perylene diimide, poly[2,7-(9,9-di-n-octylfluorene)-co-(1,4-phenylene-[(4-sec-butylphenyl)imino]-1,4-phenylene)]:perylene diimide and poly(3-hexylthiophene):([6,6]-phenylC61-butyric acid methyl ester) (P3HT:PCBM) blends has been examined up to lifetime doses equivalent to those used in medical x-ray digital imaging applications. Dark currents and external quantum efficiencies (EQEs) are not significantly affected after exposure to 500 Gy. Only in the case of P3HT:PCBM is a significant loss in EQE (17% of the initial value) observed. Possible reasons for the observed changes are proposed. When a scintillation layer is attached to the devices, a linear dependence of the photocurrent on the x-ray dose rate is observed for the three material systems. [ABSTRACT FROM AUTHOR]

Semiconducting nanowires provide routes for realizing high-performance electronic devices, but for many applications of such devices low-cost manufacturing techniques are needed. The authors demonstrate here top-gated zinc oxide nanowire field effect transistors (NW-FETs) fabricated by ink-jet printing. High resolution submicrometer gold gaps between source and drain electrodes were defined by a self-aligned ink-jet printing technique, and the nanowires were deposited from solution onto these electrode arrays and gated from the top using a spin-coated poly(methyl methacrylate) gate dielectric. The typical NW-FETs exhibited a mobility of 2–4 cm2/V s, a current on/off ratio of 104, and a transconductance of 20.5 nS. The process provides a pathway for fabrication of NW-FETs by low-cost, large-area solution processing and direct printing techniques. [ABSTRACT FROM AUTHOR]

Using a thermal-crosslinkable siloxane bisbenzocyclobutene, high quality spin-on (solutionprocessable) gate dielectric layers as thin as 50 nm have been fabricated over the semiconductor layer for polymer field-effect transistors. This was demonstrated on a poly(9,9-dialkylfluorene-alt-triarylamine) as p-channel semiconductor, with a surfactantion-exchanged poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate complex as top-gate electrode. The devices operate at a low voltage with a field-effect mobility of few 10-4 cm2/Vs, and can be continuously operated at 120 °C. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In organic device applications, a high contact resistance between metal electrodes and organic semiconductors prevents an efficient charge injection and extraction, which fundamentally limits the device performance. Recently, various contact doping methods have been reported as an effective way to resolve the contact resistance problem. However, the contact doping has not been explored extensively in organic field effect transistors (OFETs) due to dopant diffusion problem, which significantly degrades the device stability by damaging the ON/OFF switching performance. Here, the stability of a contact doping method is improved by incorporating "dopant‐blockade molecules" in the poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) film in order to suppress the diffusion of the dopant molecules. By carefully selecting the dopant‐blockade molecules for effectively blocking the dopant diffusion paths, the ON/OFF ratio of PBTTT OFETs can be maintained over 2 months. This work will maximize the potential of OFETs by employing the contact doping method as a promising route toward resolving the contact resistance problem. [ABSTRACT FROM AUTHOR]

By using the optical second harmonic generation (SHG) measurement, we directly visualized the carrier behavior leading to carrier recombination and electroluminescence (EL) in ambipolar polymer-based organic light-emitting transistor (OLET) with an active layer of poly 9,9-di-n-octylfluorene-alt-benzothiadiszole (F8BT). Eliminating photoluminescence generated at 560 nm by a two-photon absorption process, the dynamical carrier motion in the F8BT-OLET was visualized by the electric field induced SHG induced at 420 nm. Diffusion-like electron transport that starts from the drain electrode was directly caught as the transits of the SHG images. Accordingly, EL was obtained at the edge of the source electrode. The electron mobility was estimated from the visualized carrier motion as 9.2×10-4cm2/Vs, which was larger than that obtained from the transfer curve of the OLET. [ABSTRACT FROM AUTHOR]

The emission characteristics and external quantum efficiencies of ambipolar polymer light-emitting field-effect transistors are investigated as a function of applied voltage, current density, and ratio of hole to electron mobility. Green-emitting poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) with balanced electron and hole mobilities and red-emitting poly((9,9-dioctylfluorene)-2,7- diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) with strongly unbalanced hole and electron mobilities as semiconducting and emissive polymers are compared. The current-voltage and light output characteristics of the two types of light-emitting transistors were found to be fundamentally alike independent of mobility ratio. Device modeling allowing for a single (Langevin-type) charge recombination mechanism was able to reproduce the device characteristics for both cases but could not replicate the experimentally observed dependence of external quantum efficiency on current density. The increase of quantum efficiency with current density up to a saturation value could be indicative of a trap-assisted nonradiative decay mechanism at the semiconductor-dielectric interface. Optical output modeling confirmed that the maximum external quantum efficiency of F8BT light-emitting transistors of 0.8% is consistent with complete recombination of all charges and a singlet exciton fraction of 25%. [ABSTRACT FROM AUTHOR]

Keywords: 2D perovskites; metal-halide perovskites; molecular doping EN 2D perovskites metal-halide perovskites molecular doping 1 1 1 09/22/23 20230919 NES 230919 B Molecular Doping b In article number 2302048, Keehoon Kang, Takhee Lee, and co-workers demonstrate a novel immersion doping strategy for enhancing the electrical conductivity of 2D perovskites. 2D perovskites, metal-halide perovskites, molecular doping Immersion of perovskite films in dopant solution induces bulk incorporation of molecular dopants within the organic spacer layer, a strategy for which specific doping conditions for maximizing the conductivity are formulated. [Extracted from the article]

Air stable electron transport organic semiconductor was employed in inverted perovskite solar cells as a possible alternative to derivatives of fullerene. • Diketopyrrolopyrrole derivative employed as n-channel semiconductor in OFET. • TDPP-CN 4 exhibited higher electron mobility and ambient stability than PCBM. • Air stable DPP based acceptor was further employed in inverted perovskite devices. • The devices could not display competitive performance as PCBM owing to deep LUMO level. One of the possible causes of degradation of perovskite solar cells is the instability of the electron transporting layer. In this regard, design of air stable electron transport organic semiconductors, compatible with perovskite energy levels presents challenges due to inherent vulnerability to traps, presumably originating due to water and/or oxygen. In this work, we demonstrate air stability of diketopyrrolopyrrole-based molecule (TDPP-CN 4) at ambient conditions and its application as electron transporting layer (ETL) in perovskite solar cells. We investigated electron mobility and air stability of TDPP-CN 4 by fabricating top-gate bottom-contact (TG-BC) thin film transistors and compared with PCBM at ambient conditions. Both TDPP-CN 4 and PCBM exhibit electron transport properties with mobility of 0.13 cm2 V−1 s−1 and 0.03 cm2 V−1 s−1 respectively. However, we found remarkable air stability of the TDPP-CN 4 in the OFET measurements under ambient conditions. These excellent properties of TDPP-CN 4 render them as potential ETL layer in inverted planar heterojunction perovskite solar cells. Our preliminary device studies show remarkable short-circuit current (J sc) ∼ 17.4 mA/cm2 with moderate open-circuit voltage (V oc) of 0.50 V. These results suggest that the electron mobility and air-stability of diketopyrrolopyrrole-based molecule hold a promise as ETL in perovskite solar cells at ambient conditions. [ABSTRACT FROM AUTHOR]

Using a thermoelectric measurement, we demonstrate the nucleation and detection of a single 360° homochiral Néel domain wall (DW), formed by an independently nucleated pair of 180° Néel DWs having the same helicity in a perpendicular magnetic anisotropy track. The DW formation is governed by strong interfacial Dzyaloshinskii-Moriya interaction (DMI) and detected at room temperature using the anomalous Nernst effect (ANE). A large DMI can be generated at an interface where the symmetry is broken between a material having a large spin-orbit coupling and a thin ferromagnetic layer. The ANE voltage, V ANE ∝ ∇ T × M , is sensitive to the magnitude of the out-of-plane magnetization M through a confined in-plane temperature gradient ∇T and allows for the direct thermoelectrical detection of the DW position with nanoscale accuracy along the track. Here, we present evidence that independently nucleated pairs of 180° Néel DWs in microwire devices can be brought together by an applied magnetic field to form a 360° homochiral Néel DW. Subsequently, we show that a strong magnetic field needs to be applied in order to annihilate the 360° DW due to the strong interfacial DMI in our Pt/Co(0.6nm)/AlOx multilayers. In addition to enabling a high magnetic storage and data transfer rate with low power consumption in novel computational and storage devices, such DWs facilitate a reduction in bit size down to a few nanometers with metastability. [ABSTRACT FROM AUTHOR]

A novel fused heterocycle-flanked diketopyrrolopyrrole (DPP) monomer, thieno[2,3-b]pyridine diketopyrrolopyrrole (TPDPP), was designed and synthesized. When copolymerized with 3,4-difluorothiophene using Stille coupling polymerization, the new polymer pTPDPP-TF possesses a highly planar conjugated polymer backbone due to the fused thieno[2,3-b]pyridine flanking unit that effectively alleviates the steric hindrance with both the central DPP core and the 3,4-difluorothiophene repeat unit. This new polymer exhibits a high electron affinity (EA) of -4.1 eV and was successfully utilized as an n-type polymer semiconductor for applications in organic field-effect transistors (OFETs) and all polymer solar cells. A promising n-type charge carrier mobility of 0.1 cm2 V-1 s-1 was obtained in bottom-contact, top-gate OFETs, and a power conversion efficiency (PCE) of 2.72% with a high open-circuit voltage (VOC) of 1.04 V was achieved for all polymer solar cells using PTB7-Th as the polymer donor. [ABSTRACT FROM AUTHOR]

We investigate the origin of the broadband visible emission in layered hybrid lead-halide perovskites and its connection with structural and photophysical properties. We study (001) oriented thin films of hexylammonium (HA) lead iodide, (C6H16N)2PbI4, and dodecylammonium (DA) lead iodide, (C12H28N)2PbI4, by combining first-principles simulations with time-resolved photoluminescence, steady-state absorption and X-ray diffraction measurements on cooling from 300 to 4 IK Ultrafast transient absorption and photoluminescence measurements are used to track the formation and recombination of emissive states. In addition to the excitonic photoluminescence near the absorption edge, we find a red-shifted, broadband (full-width at half-maximum of about 0.4 eV), emission band below 200 K, similar to emission from (110) oriented bromide 2D perovskites at room temperature. The lifetime of this subband-gap emission exceeds that of the excitonic transition by orders of magnitude. We use X-ray diffraction measurements to study the changes in crystal lattice with temperature. We report changes in the octahedral tilt and lattice spacing in both materials, together with a phase change around 200 K in DA2PbI4. DFT simulations of the HA2PbI4 crystal structure indicate that the low-energy emission is due to interstitial iodide and related Frenkel defects. Our results demonstrate that white-light emission is not limited to (110) oriented bromide 2D perovskites but a general property of this class of system, and highlight the importance of defect control for the formation of low-energy emissive sites, which can provide a pathway to design tailored white-light emitters. [ABSTRACT FROM AUTHOR]