Single-component complementary inverters based on ambipolar organic mixed ionic-electronic conductors (OMIECs) offer promise for simplifying logic circuit design and fabrication. However, the mismatched ambipolar transport properties in OMIECs have hindered the realization of such devices. To address this challenge, we designed two ambipolar OMIECs with high-spin state: PDPPXO-2TzC4 (where X = 3, 5). These donor-acceptor (D-A) conjugated polymers were synthesized through the copolymerization of diketopyrrolopyrrole (DPP) and dialkoxybithiazole (2Tz) units, incorporating modified ethylene glycol side chains. Both materials demonstrated outstanding and relatively balanced ambipolar OECT performance, achieving an on-off ratio exceeding 105 for both p/n-type operations. PDPP3O-2TzC4 achieved normalized maximum transconductances of 0.48 S cm-1 (p-type) and 0.34 S cm-1 (n-type), while PDPP5O-2TzC4 reached 0.42 S cm-1 (p-type) and 0.29 S cm-1 (n-type). They also exhibited rapid and well-matched p-type and n-type transient responses, with time constants (τon/off) of less than 5 ms. Furthermore, leveraging the relatively balanced ambipolarity of PDPPXO-2TzC4, we fabricated functional single-component complementary inverters and obtained ternary logic characteristics under specific VDD. A biocompatibility assessment using human gingival fibroblasts (HGF) confirmed that PDPPXO-2TzC4 is suitable for biological applications, laying a foundation for future OECT devices based on these materials in logic circuits and biomedical fields.

We demonstrate here that light can be used to modulate proton transport in polymeric soft materials using a polymerizable molecular photoswitch. To this end, we design a merocyanine metastable-state photoacid, which we use as a building block to prepare a series of light-responsive polymers. We confirm the metastable character of the proposed monomer, and we elucidate its potential energy surface and the energies associated with its photoisomerization using quantum mechanical calculations. Interestingly, we found that when incorporated into a polymeric matrix, a photoacid loading effect impacts its photochromism and induces significant changes to the polymer nanostructure. Light stimulation of the films results in a reversible decrease in conductivity as the merocyanine simultaneously changes its net charge and functions as a photoacid by releasing protons, effecting switching as well as imparting proton conductivity to otherwise insulating polymers. We further exploit the commensurate changes to the polymer nanostructure to fabricate a light-driven hydrogel actuator. Our work establishes a versatile synthetic platform for the design of photo-modulated proton-conductive systems, offering new opportunities for responsive materials and iontronics applications.

Among the various n-type dopants used in organic electronics, NDMBI-H is the most common. However, precise control of the doping levels is still elusive, with reported conductivities varying by orders of magnitude for similar systems. In this study, we investigate a frequently underestimated factor: the mixing time during co-solution processing. Our focus is on a prototypical system involving NDMBI-H-doped PCBM processed in chloroform. Remarkably, we observe a decline in conductivity with prolonged mixing times that does not occur when the single components are stored individually. We establish a correlation between this behavior and characteristic signatures in the 1H NMR spectra of pristine compounds and mixtures. We attribute the decline in conductivity to the reactive nature of chloroform and extend our findings to four more organic semiconductors with different backbones. We find that choosing a suitable solvent and controlling the mixing time allow us to increase the conductivity of doped PCBM to up to 2.64 S/cm through a straightforward bulk doping process, representing a substantial improvement compared to values obtained using additives or more complex procedures.

This work experimentally investigates a mechanism of rectification in molecular junctions proposed by van Dyck and Ratner, supported by theoretical modeling. The defining feature of the mechanism is the spatial separation of frontier molecular orbitals such that each tracks the two leads independently. We achieve this orbital separation in oligophenyleneethylene molecular wires with electron-rich thiols and electron-poor pyridines at their termini. Density functional theory (DFT) calculations show localization of the frontier molecular orbitals at these termini that increases with the molecular length. Measurements of rectification ratios in molecular ensemble junctions using eutectic Ga-In (EGaIn) top-contacts and Au bottom-contacts reveal a length dependence that is almost completely insensitive to the insertion of a nonconjugated methylene spacer between the thiol anchor and conjugated backbone. Simulations using nonequilibrium Green's function + DFT methods show that transport is dominated by the lowest unoccupied molecular orbitals, which track the EGaIn electrode, leading to rectification. These results validate the approach of creating molecular rectifiers by spatially separating the frontier molecular orbitals and show an approach to modeling their behavior under bias in ensemble junctions.

This paper describes a series of four indolinooxazolidine molecular switches capable of accessing multiple distinct states by separately addressing photo- and stereo-isomerism. Photoswitches serve as valuable components in molecular devices owing to their ability to isomerize between distinct states using light as a non-invasive input. While most photoswitches are binary, converting between two states, multistate switches offer expanded operational capabilities and show promise for multi-bit architectures. We synthesized a series of four indolinooxazolidines with varied electronic structure and examined their switching behavior in different solvents. While electron-withdrawing substituents inhibit the photoisomerization pathway, the incorporation of an oligoethylene glycol chain enables both reversible photoisomerisation and acidochromic switching between six combinations of photo- and stereo-isomers.

Diffusion-based microfluidic gradient generators (DMGGs) are essential for various in-vitro studies due to their ability to provide a convection-free concentration gradient. However, these systems, often referred to as membrane-based DMGGs, exhibit delayed gradient formation due to the incorporated flow-resistant membrane. This limitation substantially hinders their application in dynamic and time-sensitive studies. Here, we accelerate the gradient response in DMGGs by removing the membrane and implementing new geometrical configurations to compensate for the membrane's role in suppressing parasitic flows. We introduce these novel configurations into two microfluidic designs: the H-junction and the Y-junction. In the H-junction design, parasitic flow is redirected through a bypass channel following the gradient region. The Y-junction design features a shared discharge channel that allows converging discharge flow streams, preventing the buildup of parasitic pressure downstream of the gradient region. Using hydraulic circuit analysis and fluid dynamics simulations, we demonstrate the effectiveness of the H-junction and Y-junction designs in suppressing parasitic pressure flows. These computational results, supported by experimental data from particle image velocimetry, confirm the capability of our designs to generate a highly stable, accurate, and convection-free gradient with rapid formation. These advantages make the H-junction and Y-junction designs ideal experimental platforms for a wide range of in-vitro studies, including drug testing, cell chemotaxis, and stem cell differentiation.

AbstractOrganic electrochemical transistors (OECTs) are of great interest in low‐power bioelectronics and neuromorphic computing, as they utilize organic mixed ionic‐electronic conductors (OMIECs) to transduce ionic signals into electrical signals. However, the poor environmental stability of OMIEC materials significantly restricts the practical application of OECTs. Therefore, the non‐fused planar naphthalenediimide (NDI)‐dialkoxybithiazole (2Tz) copolymers are fine‐tuned through varying ethylene glycol (EG) side chain lengths from tri(ethylene glycol) to hexa(ethylene glycol) (namely P‐XO, X = 3–6) to achieve OECTs with high‐stability and low threshold voltage. As a result, the NDI‐2Tz copolymers exhibit ambipolarity, rapid response (<10 ms), and ultra‐high n‐type stability. Notably, the P‐6O copolymers display a threshold voltage as low as 0.27 V. They can operate in n‐type mode in an aqueous solution for over 60 h, maintaining an on‐off ratio of over 105. This work sheds light on the design of exceptional n‐type/ambipolar materials for OECTs. It demonstrates the potential of incorporating these ambipolar polymers into water‐operational integrated circuits for long‐term biosensing systems and energy‐efficient brain‐inspired computing.

Self-assembled monolayers of alkanethiols on gold are often used as a benchmark for molecular junctions, particularly as a reference for length-dependence. However, their thermopower decreases with molecular length and is bifurcated. While the bifurcation can be explained by the presence of gateway states, the length-dependence directly contradicts theoretical predictions. We reproduced both experimentally using conical tips of eutectic Ga-In (EGaIn) to form junctions. We then show that this unusual length-dependence arrises from the direction of the applied thermal gradient; when the gold substrate is cooled instead of heated, thermopower increases with length monotonically as predicted by theory. This unprecedented relationship between length-dependence and direction of thermal gradient persists over a very large range of absolute temperature. We therefore ascribe it to shifts in level-alignment induced by the electric field in the leads, which is present experimentally, neglected in theoretical modeling and is determined by the direction of the thermal gradient.

Molecular doping is a key strategy to enhance the electrical conductivity of organic semiconductors. Typically, the electrical conductivity shows a maximum value upon increased doping, after which the conductivity decreases. This decrease in conductivity is commonly attributed to unfavorable changes in the morphology. However, in recent simulation work, has shown, that the conductivity-at high doping-is instead limited by electron-electron repulsion rather than by morphology, at least for some material combinations. Based on the simulations, this limitation is expected to show up in the dependence of the Seebeck coefficient versus carrier density: the Seebeck coefficient will follow Heike's formula if carrier-carrier repulsion limits the conductivity. Here, the electrical conductivity and Seebeck coefficient are measured as a function of doping for a series of n-type organic semiconductors. Additionally, the resulting carrier density is measured using metal-insulator-semiconductor diodes, which link dopant loading and the number of charge carriers. At high carrier densities, the Seebeck coefficient indeed follows Heike's formula, confirming that the conductivity is limited by carrier-carrier repulsion rather than by morphological effects. This study shows that current models of hopping transport in organic semiconductors may be incomplete. As a result, this study offers novel insights in the design of organic semiconductors.

We measured the Seebeck coefficient for junctions comprising self-assembled monolayers and bilayers of the fullerene moiety PTEG-1 on Au using eutectic Ga-In in a controlled anhydrous atmosphere by varying the temperature gradient from -12 to 12 degrees C, observing a linear response in thermovoltage across the range. The sign of the coefficient was positive for monolayers of PTEG-1, (195 +/- 8) mu V K-1 and negative for bilayers of PTEG-1, (-209 +/- 14) mu V K-1, indicating a change from HOMO-mediated to LUMO-mediated charge-transport. Charge-transport is nonresonant tunneling for both monolayers and bilayers, but the former self-assembles with the fullerene cage at the chemisorbed interface while the latter includes a fullerene cage at the physisorbed interface, demonstrating that the physical position of the fullerene cage determines the energetic position of the frontier molecular orbitals of PTEG-1.

Organic thermoelectric materials have garnered significant interest as promising candidates for energy harvesting applications. In recent years, ethylene-glycol side-chain engineering in organic semiconductors has gradually become an efficient approach to boost the performance of organic thermoelectrics. Although this strategy is widely utilized, the impact of their volume and branching structure remains unknown. This contribution describes a trade-off phenomenon between the oligo(ethylene glycol) (OEG) side chains and thermoelectric properties based on the n-type doped low-bandgap conjugated polymers, achieved through the modification of the volume and structure of side chains. Three conjugated polymers comprising a naphthalenediimide-dialkoxybithiazole backbone and different linear length or branched OEG side chains exhibit good host/dopant miscibility after doping. We find that, in the linear OEG side-chain-based polymers, the increased volume of side chains slightly influences the planarity of backbones, thereby leading to similar and satisfactory thermoelectric performances. The high fraction of side chains does not consistently yield enhanced performance, as the branched OEG side-chain introduces steric hindrance. Consequently, the accordingly conjugated backbones become less planar and rigid, resulting in critical molecular packing changes and low charge carrier mobility and doping efficiency and thus low thermoelectric performance. Our work provides a unique insight into the fundamental understanding of the relationship between molecular packing and thermoelectric properties and guides the future rational design of efficient n-type organic semiconductors.

This paper describes large-area molecular tunneling junctions comprising self-assembled monolayers (SAMs) of light-harvesting protein complexes using eutectic Ga-In (EGaIn) as a top contact. The complexes, which are readily isolable in large quantities from spinach leaves, self-assemble on top of SAMs of [6,6]-phenyl-C61-butyric acid (PCBA) on gold (Au) supported by mica substrates (AuMica), which induces them to adopt a preferred orientation with respect to the electron transport chain that runs across the short axis of each complex, leading to temperature-independent rectification. We compared trimeric protein complexes isolated from thermophilic cyanobacteria to monomeric complexes extracted from spinach leaves by measuring charge-transport at variable temperatures and over the course of at least three months. Transport is independent of temperature in the range of 130 to 310 K for both protein complexes, affirming that the likely mechanism is non-resonant tunneling. The junctions rectified current and were stable for at least three months when stored at room temperature in ambient conditions, with the yield of working junctions falling from 100% to 97% over that time. These results demonstrate a straightforward strategy for forming remarkably robust molecular junctions, avoiding the fragility that is common in molecular electronics. This paper describes large-area molecular tunneling junctions comprising self-assembled monolayers (SAMs) of light-harvesting protein complexes using eutectic Ga-In (EGaIn) as a top contact.

Recently, carbazole‐based self‐assembled monolayers (SAMs) have been utilized as hole transport layers (HTLs) in perovskite solar cells. However, their application in Sn or mixed Sn/Pb perovskite solar cells has been hindered by the poor wettability of the perovskite precursor solution on the carbazole surface. Here a self‐assembled bilayer (SAB) comprising a covalent monolayer (Br‐2PACz) and a noncovalent wetting layer (4CzNH 3 I) as the HTL in a Cs 0.25 FA 0.75 Sn 0.5 Pb 0.5 I 3 perovskite solar cell is proposed. It is demonstrated that the wetting layer completely solves the problem due to the higher polarity of the surface and, furthermore, the ammonium groups help in the passivation of trap states at the buried SAB/perovskite interface. The introduction of the SAB enhances the device reproducibility with an average efficiency of 18.98 ± 0.28% (19.45% for the best device), compared to 11.54 ± 9.36% (19.34% for the best device) for the SAM‐only devices. Furthermore, the improved perovskite processability on the SAB helps to increase the reproducibility of larger size device, where, a 12.5% efficiency for a 0.8 cm 2 active area device compared to 0.68% for the best SAM‐based solar cell is demonstrated. Finally, the device's operational stability is also improved to 358 hours (T 80% ), compared to 220 hours for the SAM‐based solar cell.

This work describes the effects of dodecavanadate anions and phthalocyanine ligands as well as the identity of lanthanide centers on the charge transport characteristics of heterometallic complexes (nBu(4)N)(3)[HV12O32Cl(LnPc)] and (nBu(4)N)(2)[HV12O32Cl(LnPc)(2)] for Sm-III-Er-III, Lu-III, and Y-III on gold surfaces. In molecular ensemble junctions with eutectic Ga-In top contacts, the complexes containing two phthalocyanine ligands are highly conductive but show no clear effect of varying the lanthanide. By contrast, the complexes that omit phthalocyanine but include 4f-functionalized dodecavanadate building blocks show clear trends in conductance, rectification, and transition voltages. Density functional theory calculations show that the occupied and unoccupied frontier orbitals in the heterometallic complexes are delocalized on the phthalocyanine ligand and dodecavanadate anion, respectively, suggesting strong lanthanide-ligand electronic coupling. Near-edge X-ray absorption fine structure spectroscopy on these complexes further suggests that the phthalocyanine ligands are arranged such that their edges are in contact with the electrodes, creating tunneling transmission channels that bypass the lanthanide, effectively obviating the electronic contributions of the lanthanide centers to charge transport. These results separate the influence of the individual constituents of these metal-ligand complexes on the tunneling charge-transport properties. These results demonstrate how strongly coupled ligands such as phthalocyanine can dominate charge transport, from which we construct design rules for harnessing the properties of f-block elements in redox-active molecular heterojunctions.

Doping to enhance the electrical conductivity of organic semiconductors is not without its challenges: The efficacy of this process depends on many factors and it is not always clear how to remedy poor doping. In the case of doping with salts, one of the possible causes of poor doping is a limited yield of integer charge transfer resulting in the presence of both cations and anions in the film. The charge of such ions can severely limit the electrical conductivity, but their presence is not easily determined. Here we introduce a set of simple conductivity measurements to determine whether poor doping in the case where the dopant is a salt is due to limited integer charge transfer. By tracking how the conductivity changes over time when applying a bias voltage for an extended amount of time we can pinpoint whether unwanted ions are present in the film. Firstly, we introduce the principle of this approach by performing numerical simulations that include the movement of ions. We show that the conductivity can increase or decrease depending on the type of ions present in the film. Next, we show that the movement of these dopant ions causes a build-up of space-charge, which makes the current-voltage characteristic non-linear. Next, we illustrate how this approach may be used in practice by doping a fullerene derivative with a series of organic salts. We thus provide a tool to make the optimization of doping more rational.

This paper describes the fabrication of digital logic circuits comprising resistors and diodes made from protein complexes and wired together using printed liquid metal electrodes. These resistors and diodes exhibit temperature-independent charge-transport over a distance of approximately 10 nm and require no encapsulation or special handling. The function of the protein complexes is determined entirely by self-assembly. When induced to self-assembly into anisotropic monolayers, the collective action of the aligned dipole moments increases the electrical conductivity of the ensemble in one direction and decreases it in the other. When induced to self-assemble into isotropic monolayers, the dipole moments are randomized and the electrical conductivity is approximately equal in both directions. We demonstrate the robustness and utility of these all-protein logic circuits by constructing pulse modulators based on AND and OR logic gates that function nearly identically to simulated circuits. These results show that digital circuits with useful functionality can be derived from readily obtainable biomolecules using simple, straightforward fabrication techniques that exploit molecular self-assembly, realizing one of the primary goals of molecular electronics.

This paper describes the use of reduced graphene oxide decorated with gold nanoparticles as an efficient electron transfer layer for solid-state biophotovoltic cells containing photosystem I as the sole photo-active component. Together with polytyrosine-polyaniline as a hole transfer layer, this device architecture results in an open-circuit voltage of 0.3 V, a fill factor of 38% and a short-circuit current density of 5.6 mA cm-2 demonstrating good coupling between photosystem I and the electrodes. The best-performing device reached an external power conversion efficiency of 0.64%, the highest for any solid-state photosystem I-based photovoltaic device that has been reported to date. Our results demonstrate that the functionality of photosystem I in the non-natural environment of solid-state biophotovoltaic cells can be improved through the modification of electrodes with efficient charge-transfer layers. The combination of reduced graphene oxide with gold nanoparticles caused tailoring of the electronic structure and alignment of the energy levels while also increasing electrical conductivity. The decoration of graphene electrodes with gold nanoparticles is a generalizable approach for enhancing charge-transfer across interfaces, particularly when adjusting the levels of the active layer is not feasible, as is the case for photosystem I and other biological molecules.

Organic mixed ionic-electronic conductors (OMIECs) are central to bioelectronic applications such as biosensors, health-monitoring devices, and neural interfaces, and have facilitated efficient next-generation brain-inspired computing and biohybrid systems. Despite these examples, smart and adaptive circuits that can locally process and optimize biosignals have not yet been realized. Here, a tunable sensing circuit is shown that can locally modulate biologically relevant signals like electromyograms (EMGs) and electrocardiograms (ECGs), that is based on a complementary logic inverter combined with a neuromorphic memory element, and that is constructed from a single polymer mixed conductor. It is demonstrated that a small neuromorphic array based on this material effects high classification accuracy in heartbeat anomaly detection. This high-performance material allows for straightforward monolithic integration, which reduces fabrication complexity while also achieving high on/off ratios with excellent ambient p- and n-type stability in transistor performance. This material opens a route toward simple and straightforward fabrication and integration of more sophisticated adaptive circuits for future smart bioelectronics.

In recent years, the dielectric constant (εr) of organic semiconductors (OSCs) has been of interest in the organic photovoltaic (OPV) community due to its potential influence on the exciton binding energy. Despite progress in the design of high εr OSCs and the accurate measurement of the εr, the effects of the synthetic strategies on specific (opto)electronic properties of the OSCs remain uncertain. In this contribution, the effects of εr on the optical properties of five new C70 derivatives and [70]PCBM are investigated. Together with [70]PCBM, the derivatives have a range of εr values that depend on the polarity and length of the side chains. The properties of the singlet excitons are investigated in detail with steady-state and time-resolved spectroscopy and the exciton diffusion length is measured. All six derivatives show similar photophysical properties in the neat films. However, large differences in the crystallinity of the fullerene films influence the exciton dynamics in blend films. This work shows that design principles for OSCs with a higher εr can have a very different influence on the performance of traditional BHJ devices and in neat films and it is important to consider the neat film properties when investigating the optoelectronic properties of new materials for OPV.

Conjugated polymers with narrow band gaps are particularly useful for sorting and discriminating semiconducting single-walled carbon nanotubes (s-SWCNT) due to the low charge carrier injection barrier for transport. In this paper, we report two newly synthesized narrow-band-gap conjugated polymers (PNDITEG-TVT and PNDIC8TEG-TVT) based on naphthalene diimide (NDI) and thienylennevinylene (TVT) building blocks, decorated with different polar side chains that can be used for dispersing and discriminating s-SWCNT. Compared with the mid-band-gap conjugated polymer PNDITEG-AH, which is composed of naphthalene diimide (NDI) and head-to-head bithiophene building blocks, the addition of a vinylene linker eliminates the steric congestion present in head-to-head bithiophene, which promotes backbone planarity, extending the π-conjugation length and narrowing the band gap. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest that inserting a vinylene group in a head-to-head bithiophene efficiently lifts the highest occupied molecular orbital (HOMO) level (-5.60 eV for PNDITEG-AH, -5.02 eV for PNDITEG-TVT, and -5.09 eV for PNDIC8TEG-TVT). All three polymers are able to select for s-SWCNT, as evidenced by the sharp transitions in the absorption spectra. Field-effect transistors (FETs) fabricated with the polymer:SWCNT inks display p-dominant properties, with higher hole mobilities when using the NDI-TVT polymers as compared with PNDITEG-AH (0.6 cm2 V-1 s-1 for HiPCO:PNDITEG-AH, 1.5 cm2 V-1 s-1 for HiPCO:PNDITEG-TVT, and 2.3 cm2 V-1 s-1 for HiPCO:PNDIC8TEG-TVT). This improvement is due to the better alignment of the HOMO level of PNDITEG-TVT and PNDIC8TEG-TVT with that of the dominant SWCNT specie.