This PDF file contains the front matter associated with SPIE Proceedings Volume 9568, including the Title Page, Copyright information, Table of Contents, Authors, and Conference Committee listing.

Organic transistors with vertical current transport like the Permeable Base Transistor (PBT) show a high performance while allowing for an easy fabrication on the device level. For a simple implementation on a circuit level, ambipolar transistors, providing the functionality of n-type as well as p-type devices, have a benefit for complementary logic. This requires transistors where electrons and holes are present. Here, we investigate a potential concept of bipolar current transport in PBTs. In our device structure, we use the base electrode to control the current flow, but also to investigate the charge carrier transport. The ambipolar organic PBT achieves a charge carrier transmission of 88% and a current density above 200mA=cm². Additionally, we show that recombination near the base is required in an ambipolar PBT for a good performance.

Organic light-emitting diodes (OLEDs) are well studied and established in current display applications. Light-emitting transistors (LETs) have been developed to further simplify the necessary circuitry for these applications, combining the switching capabilities of a transistor with the light emitting capabilities of an OLED. Such devices have been studied using mono- and bilayer geometries and a variety of polymers [1], small organic molecules [2] and single crystals [3] within the active layers. Current devices can often suffer from low carrier mobilities and most operate in p-type mode due to a lack of suitable n-type organic charge carrier materials. Hybrid light-emitting transistors (HLETs) are a logical step to improve device performance by harnessing the charge carrier capabilities of inorganic semiconductors [4]. We present state of the art, all solution processed hybrid light-emitting transistors using a non-planar contact geometry [1, 5]. We will discuss HLETs comprised of an inorganic electron transport layer prepared from a sol-gel of zinc tin oxide and several organic emissive materials. The mobility of the devices is found between 1-5 cm2/Vs and they had on/off ratios of ~105. Combined with optical brightness and efficiencies of the order of 103 cd/m2 and 10-3-10-1 %, respectively, these devices are moving towards the performance required for application in displays. [1] M. Ullah, K. Tandy, S. D. Yambem, M. Aljada, P. L. Burn, P. Meredith, E. B. Namdas., Adv. Mater. 2013, 25, 53, 6213 [2] R. Capelli, S. Toffanin, G. Generali, H. Usta, A. Facchetti, M. Muccini, Nature Materials 2010, 9, 496 [3] T. Takenobu, S. Z. Bisri, T. Takahashi, M. Yahiro, C. Adachi, Y. Iwasa, Phys. Rev. Lett. 2008, 100, 066601 [4] H. Nakanotani, M. Yahiro, C. Adachi, K. Yano, Appl. Phys. Lett. 2007, 90, 262104 [5] K. Muhieddine, M. Ullah, B. N. Pal, P. Burn E. B. Namdas, Adv. Mater. 2014, 26,37, 6410

While much of the OTFT activity has been display-centric there is no doubt that as the OTFT technology matures the number of applications will continue to increase. Using our most recent flexible X-ray detectors we will discuss the prospect and challenges of organic transistors in sensor backplanes. For these application, the current mobility of ~0.1-2 cm2/Vs of OTFTs is currently not a problem. Their low leakage currents give them a distinct advantage over competing technologies, such as amorphous silicon TFT. Yet, challenges remain and these will be discussed.

We demonstrate top-gate organic field-effect transistors (OFETs) with a bilayer gate dielectric and doped contacts fabricated on shape-memory polymer (SMP) substrates. SMPs exhibit large variations in Young’s modulus dependent on temperature and have the ability to fix two or more geometric configurations when a proper stimulus is applied. These unique properties make SMPs desirable for three-dimensional shape applications of OFETs. The electrical properties of OFETs on SMP substrates are presented and compared to those of OFETs on traditional glass substrates.

Efficient local transduction of biological signals is of critical importance for mapping brain activity and diagnosing pathological conditions. Traditional devices used to record electrophysiological signals are passive electrodes that require (pre)amplification with downstream electronics. Organic electrochemical transistors (OECTs) that utilize conducting polymer films as the channel have shown considerable promise as amplifying transducers due to their stability in aqueous conditions and high transconductance (>3 mS). The materials properties and physics of such transistors, however, remains largely unexplored thus limiting their potential. Here we show that the uptake of ionic charge from an electrolyte into a poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) OECT channel leads to a dependence of the effective capacitance on the entire volume of the film. Subsequently, device transconductance and time response vary with channel thickness, a defining characteristic that differentiates OECTs from field effect transistors, and provides a new degree of freedom for device engineering. Using this understanding we tailor OECTs for a variety of low (1-100 Hz) and high (1-10 kHz) frequency applications, including human electroencephalography, where high transconductance devices impart richer signal content without the need for additional amplification circuitry. We also show that the materials figure of merit OECTs is the product of hole mobility and volumetric capacitance of the channel, leading to design rules for novel high performance materials.

The boom in multifunctional, flexible, and portable electronics and the increasing need of low-energy cost and autonomy for applications ranging from wireless sensor networks for smart environments to biomedical applications are triggering research efforts towards the development of self-powered sustainable electronic devices. Within this context, the coupling of electronic devices (e.g. sensors, transistors) with small size energy storage systems (e.g. micro-batteries or micro-supercapacitors) is actively pursued. Micro-electrochemical supercapacitors are attracting much attention in electronics for their capability of delivering short power pulses with high stability over repeated charge/discharge cycling. For their high specific pseudocapacitance, electronically conducting polymers are well known as positive materials for hybrid supercapacitors featuring high surface carbon negative electrodes. The processability of both polymer and carbon is of great relevance for the development of flexible miniaturised devices. Electronically conducting polymers are even well known to feature an electronic conductivity that depends on their oxidation (p-doped state) and that it is modulated by the polymer potential. This property and the related pseudocapacitive response make polymer very attracting channel materials for electrolyte-gated (EG) transistors. Here, we propose a novel concept of “Trans-capacitor”, an integrated device that exhibits the storage properties of a polymer/carbon hybrid supercapacitor and the low-voltage operation of an electrolyte-gated transistor.

Organic thin films based on composite materials of semiconducting dibenzo-tetrathiafulvalene (DB-TTF) and insulating styrenic matrices (Polystyrene (PS10k) and Poly-alpha methylstyrene (PAMS10k) ) have been fabricated by the wire-bar coating technique in ambient conditions (air, light, humidity) and contrasted with the ones prepared by thermally evaporating the organic semiconductor. The transistors fabricated with DB-TTF:PS10k composites show a clear fieldeffect behavior with p-type characteristics, exhibiting charge carriers mobilities in the range of 0.01 cm²/Vs, fully comparable with the films obtained by thermal evaporation. However, while the thermally evaporated films show poor stability in air, the wire-bar coated composites films and devices are highly reproducible and exhibit lower threshold voltage values. Thus, we demonstrate the suitability of the wire-bar technique for manufacturing large area devices.

We present the structural, optical, and electronic properties of two polymorphs of the charge-transfer complex dibenzotetrathiafulvalene-7,7,8,8-tetracyanoquinodimethane (DBTTF-TCNQ). The structures were resolved using electron diffraction. One is a rectangular-shaped platelet and exhibits ambipolar transport with gold contacts in organic field-effect transistors (OFETs). The second polymorph grows as a thin, circular platelet and shows p-type transport within the same OFET structure. The difference in electrical characteristics originates from two factors. First, the position of the HOMO level of the rectangular polymorph lies 0.07 eV below that of the circular polymorph, as determined by ultraviolet photoelectron spectroscopy (UPS). Second, using X-Ray photoelectron and Raman spectroscopies we find that the degree of charge transfer between the donor DBTTF and acceptor TCNQ varies from 0.4e ± 0.1e for the rectangular crystals to 0.1e ± 0.1e for the circular crystals. Additional differences between the two polymorphs arise when measuring the absorbance of the crystals. First, the peak corresponding to intermolecular charge transfer is offset by 0.05 eV between the two polymorphs, in agreement with UPS measurements. Additionally, the polarization angle dependence of the intermolecular CT band for the rectangular crystal is shifted by 60deg with respect to the angle dependence of the intramolecular transition. In contrast, this shift was only 20deg for the circular polymorph. These angle dependences allowed us to couple the anisotropy of the electrical characteristics to the optical measurements. Our results demonstrate how slight modifications in crystal structure yield drastic differences in optical and electrical properties in organic semiconducting materials.

For the real application of organic electronics, stable operation of electronic devices in humid or aqueous condition is essential and desirable. However, most of organic semiconductors were very weak to the oxygen or water and especially, cannot be operated well in aqueous condition without an encapsulation. Here, we present water-stable organic thin-film transistors with highly crystallized rubrene and polymer-treated dielectrics. These high water-stability could be achieved by two factors. First, rubrene, a well-known p-type semiconducting material, showed high air and water stability after the crystallization of ‘abrupt heating’. By the fabrication and aqueous operation of rubrene thin film transistor, we could show the water stability of crystallized thin-film rubrene. Such high environmental stability is attributed to the fact that rubrene has comparatively low HOMO level of -5.4 eV and large bandgap energy of 3.2 eV and that the rubrene thin-film is composed of well-interconnected orthorhombic rubrene crystals. Second, the polymer-treatment of dielectrics can enhance long-term water stability of fabricated rubrene thin-film transistor. By the complete immersion test of transistors, we could characterize the increase of water-stability after the treatment of dielectrics with cross-linked polymer. For this purpose, polystyrene is cross-linked by electron irradiation and the water penetration into semiconductor/dielectric interface was decreased due to the decreased surface energy of polymer dielectric compared to the SiO₂. The fabricated rubrene thin-film transistors showed a field-effect mobility of ~0.5 cm²V^-1s^-1 and long-term stability under ambient and aqueous conditions. Also, we investigated their potential applications in chemical or bio sensors.

Here we present and discuss our recent investigations into the understanding of microscopic charge transport, novel film processing technologies, and a development of layered-crystalline organic semiconductors for high performance OTFTs. We first discuss the microscopic charge transport in the OTFTs, as investigated by field-induced electron spin resonance spectroscopy. The technique can detect signals due to tiny amount of field-induced carriers, accumulated at the semiconductor-insulator interfaces. Following aspects are presented and discussed; 1) Carrier motion within the crystalline domains can be understood in terms of the trap-and-release transport, 2) charge trap states are spatially extended over several sites depending on the trap levels, and 3) the intra- and inter-domain transport can be discriminated by anisotropic electron spin resonance measurements. Next we discuss novel print production technologies for organic semiconductors showing high layered crystallinity. The concept of “printed electronics” is now regarded as a realistic paradigm to manufacture light-weight, thin, and impact-resistant electronics devices, although production of highly crystalline semiconductor films may be incompatible with conventional printing process. We here present printing techniques for manufacturing high performance OTFTs; 1) double-shot inkjet printing for small-molecule-based semiconductors, and 2) push-coating for semiconducting polymers. We demonstrate that both processes are useful to manufacture high quality semiconductor layers with the high layered crystallinity.

The mechanism of high field-effect mobility observed recently in transistors with donor-acceptor alternating polymers was experimentally and numerically examined. It was revealed that the trapped electrons injected from the drain electrode into the lowest unoccupied molecular orbital states of semiconductor polymers cause a deviation from the ideal transistor curve and result in an overestimation of hole mobilities. The field-effect mobility of 19 cm²/Vs was deduced by the standard formula for extracting mobility in the saturation regime after electron trapping, while the true mobility of 0.84 cm²/Vs was extracted before electron trapping.

In this work, we investigated the electrical characteristics of pentacene-based ambipolar organic thin-film transistors (OTFTs) by modifying the channel length. We fabricated a top contact device structure with sliver as the source and drain electrodes and heavy doped p-type silicon wafer as the gate electrode. The channel length of the pentacene-based ambipolar OTFTs are 50, 100, 250, and 400 μm; the channel width is fixed. The output current of the n-channel and p-channel decreases with increasing channel length. The saturated mobility and threshold voltage of both channels increase with the increase in channel length. The increase rate of saturated mobility and threshold voltage of the n-channel is larger than that of the p-channel. The influence of channel length on the electrical properties of the p-channel and n-channel is different. We utilized the gated-transfer length method to study the contact resistance between sliver and pentacene and the channel resistance of pentacene. Contact and channel resistance decrease with the increase in gate voltage in the saturation region. The total resistance of pentacene-based ambipolar OTFTs increases with channel length at a fixed gate voltage. However, n-channel total resistance has stronger gate voltage and channel length dependence than p-channel total resistance. This result reveals that electron transport in the device channel requires a larger driving voltage than in the hole. Selecting a suitable channel length is critical to obtain a well-balanced performance of the dual carriers that transport ambipolar OTFTs and to avoid a large loss in injection barrier.

High-resolution features are key to achieve high performance printed electronics devices such as transistors. Gravure printing is very promising to achieve high resolution in combination with high printing speeds on the order of 1m/s. High-speed gravure has recently been shown to print high resolution features down to linewidths and spacing of 2μm. Whilst this was a tremendous improvement over previous reports, these results had been obtained using silicon printing plates. These silicon printing plates are fabricated using microfabrication techniques which offer several advantages over traditional metal gravure cylinders where the features are defined by techniques such as stylus engraving, laser engraving or etching. This offers much greater precision and design freedom in terms of feature size, surface roughness, cell placement and cell shape. However, rigid silicon printing plates cannot be used in a roll-to-roll printing process that would truly enable low-cost printed electronics. Here we demonstrate for the first time a gravure printing roll that combines the precision of silicon printing plates with the form factor of a metal cylinder. The fabrication process starts with a silicon master whose pattern is replicated by polymer molding. The actual metal printing plate is then built up on the polymer negative of the pattern by a combination of electroless and electroplating. After separation of the polymer and the metal, the metal printing plate can be mounted on a magnetic roll for printing. Printing of highly scaled 2μm features is demonstrated. Different metal surfaces were explored to optimize printing performance and wear during printing.

Novel, extremely narrow band-gap polymer with a structure based on natural indigo has been synthesised and exhibits high crystallinity, high ambipolar transport in OFET devices, and OPV device efficiencies up to 2.35% with light absorbance up to 950 nm, demonstrating potential in near-IR photovoltaics. We demonstrate that the use of a potentially bio-sustainable monomer unit in a conjugated polymer can give balanced ambipolar OFET mobilities in excess of 0.5 cm2/Vs. This novel monomer, and polymers are synthesized by rigidifying the structure of indigo by condensation with an aromatic acidic acid. The materials display high crystallinity which can be further enhanced by annealing and demonstrate that it can be used as a potentially biosustainable alternative to the commonly used DPP and iso-indigo monomers. We believe this is the first attempt to tackle the issue of sustainability in conjugated polymer synthesis.

Diketopyrrolopyrrole (DPP)-based copolymers, including poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-(E)-1,2-di(2,2’-bithiophen-5-yl)ethene (PDDBE) and poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-(E)-1,2-bis(6-hexylthieno[3,2-b]thiophene-2-yl)ethene (PDTTE), were synthesized by alternating a DPP-derivative acceptor (A) block with different donor (D) blocks, such as (E)-1,2-di(2,2’-bithiophen-5-yl)ethene and (E)-1,2-bis(6-hexylthieno[3,2-b]thiophene-2-yl)ethene. These copolymers had drastically different crystal structures on polymer-grafted SiO2 dielectrics. Multiple-layered crystallites of PDDBE had a long-range, π-conjugated extension but a wide conjugated distance, d(010), of 3.90 Å. Nanorod-percolated agglomerates of PDTTE had a much shorter d(010) of 3.71 Å, originating from the alternating structures of the DPP derivative with slightly different D blocks. The corresponding crystallites yielded a wide range of mobilities from 0.01 to 1.40 cm2V-1s-1 in the OFETs.

Charge transport in conjugated polymers has a complex dependence on film morphology. Aligning the polymer chains in the plane of the film simplifies the morphology of the system allowing for insight into the morphological dependence of charge transport. Highly aligned conjugated polymers have also been shown to lead to among the highest reported field effect mobilities in these materials to date. In this talk, a comparison will be made between aligned polymer films processed using two primary methods, nanostructured substrate assisted growth and mechanical strain. A number of polymer systems including P3HT, pBTTT, N2200, and PCDTPT are considered, and the processed films are analyzed in detail with optical spectroscopy, AFM, TEM, and X-ray scattering providing insight into the molecular features that allow for effective alignment. By contrasting the morphology of these films, several insights into underlying charge transport limitations can be made. A number of key morphological features that lead to high field effect mobility and charge transport anisotropy in these films will be discussed. In addition, several unique features of organic thin film transistor device behavior in these systems will be examined including the commonly observed gate voltage dependence of saturated field effect mobility.

Semiconducting polymers play an important role in a wide range of optical and electronic material applications. Polymer thin films that result in the highest performance typically have a complex semicrystalline morphology, indicating that considerable device improvement can be achieved through optimization of microstructural properties. However, the connection between molecular ordering and device performance is difficult to predict due to the current need for a mathematical theory of the physics that dictates charge transport in semiconducting polymers. It is experimentally suggested that efficient transport in such films occurs via connected networks of crystallites. We present an analytical and computational description of semicrystalline conjugated polymer materials that captures the impact of polymer conformation on charge transport in heterogeneous thin films. We first develop an analytical theory for the statistical behavior of a polymer emanating from a crystallite and predict the average distance to the first kink in the chain that traps a charge. We use this analysis to define the conditions for percolation and the consequent efficient transport through a semicrystalline material. We then establish a charge transport model using Monte Carlo simulations that predicts the multi-scale charge transport and crystallite connections. We approximate the thin film as a two-dimensional grid of crystallites embedded in amorphous polymer. The chain conformations in the amorphous region are determined by the wormlike chain model, and the crystallites are assigned fixed mobilities. We use this model to identify limits of charge transport at various time scales for varying fraction of crystallinity.

Plastic electronics that can be manufactured using solution-based methods are the subject of great research interest due to their potential for low-cost, large-area electronic applications. The interest in this field has led to considerable research and subsequent advances in device performance. To this end solution-processed organic thin-film transistors (OTFTs) have shown impressive improvements in recent years through the increasing values of charge carrier mobility. Here we report the development of next generation organic blend materials for OTFTs with hole mobilities of 10 cm2/Vs. These high performance devices have been achieved using a novel semiconducting blend system comprising of an amorphous-like conjugated polymer and a high mobility small molecule. The combination of a highly crystalline small molecule with the polymer binder aids the formation of uniform films as well as enables an element of control over the nucleation and growth of the small molecule. The polymer binders investigated belongs to the family of indacenodithiophene-based copolymers which are renowned for their high carrier mobilities regardless of their apparent structural disorder. The addition of the polymer with carefully chosen small molecules is found to further increase the hole mobility of the resulting blend OTFT to over 10 cm2/Vs. These organic devices provide an interesting insight into this rather complex blend system, highlighting the correlation between the morphology developed following solution processing and device performance, as well as exploring the role of each of the two components in the blend in terms of their contribution to charge transport.

A novel fast, easily processible and highly reproducible approach to thiophene-based monolayer OFETs fabrication by Langmuir-Blodgett or Langmuir-Schaefer techniques was developed and successfully applied. It is based on selfassembly of organosilicon derivatives of oligothiophenes or benzothienobenzothiophene on the water-air interface. Influence of the conjugation length and the anchor group chemistry of the self-assembling molecules on the monolayer structure and electric performance of monolayer OFETs was systematically investigated. The efficient monolayer OFETs with the charge carrier mobilities up to 0.01 cm²/Vs and on/off ratio up to 10⁶ were fabricated, and their functionality in integrated circuits under normal air conditions was demonstrated.

Organic vertical field effect transistors (VFETs) have been explored to enhance the output current level and device operation speed due to the inherent low carrier mobility of organic semiconductors. However, most of VFETs reported to date involve a complex source electrode patterning process owing to their operation mechanism. Here, we investigate on VFETs based on C60 that do not require complex source electrode patterning process by insulting the top surface of a source electrode embedded in C60 layer [1]. In a VFET structure studied in this work, current flow is controlled by the electric field between a gate and a source electrode embedded within an active layer which is called bottom active layer. Based on its operation mechanism, several geometrical parameters such as (i) bottom active layer thickness; (ii) presence of a charge blocking layer and its thickness ensuring insulating properties; and (iii) the width of electrodes are identified as key factors influencing device performance. Through the device optimization with these parameters, the proposed organic VFETs exhibit a large on/off ratio of 6×10^5 and output current that is greater than that of a conventional C60 based OTFT with a similar device dimension. In order to show the benefit of VFETs, a single-pixel organic light-emitting diode (OLED) is integrated vertically with the VFETs under study.

We described the effect of the ultraviolet ozone (UVO) treatment of a polydimethylsiloxane (PDMS) stamp on the fidelity of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) patterns produced from a TIPS-PEN/polymer blend by selective contact evaporation (SCE). During the SCE process, the TIPS-PEN in contact with the nanoporous PDMS was absorbed into the PDMS stamp, leaving out the TIPS-PEN patterns, complementary to the PDMS patterns, in the non-contact regions. For the case of the untreated, hydrophobic PDMS surface, the TIPS-PEN patterns developed initially were shrunken and eventually disappeared after 24 h due to the steady absorption of the TIPS-PEN in time. In contrast, for the UVO-treated case, the TIPS-PEN patterns were found to maintain the initial shapes over the period of 24 h since the absorption of the TIPS-PEN was limited by the hydrophilic nature of the UVO-treated PDMS. The modified PDMS surface by the UVO for 30 min yielded the highest fidelity of the TIPS-PEN patterns in both height and width. The patterned TIPS-PEN layer by the SCE was implemented into an organic field-effect transistor to demonstrate the viability of the SCE combined with the UVO treatment for solution-processed organic electronic devices.

We report on enhanced performance in poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic field effect transistors (OFETs) achieved by improvement in hole transport along the channel near the insulator/semiconductor (I/S) interface. The improvement in hole transport is demonstrated to occur very close to the I/S interface, after treatment of the insulator layer with sodium dodecyl sulfate (SDS). SDS is an anionic surfactant, with negatively charged heads, known for formation of micelles above critical micelle concentration (CMC), which contribute to the passivation of positively charged traps. Investigation of field-effect mobility (μ_FET) as a function of channel bottleneck thickness in OFETs reveals the favorable gate voltage regime where mobility is the highest. In addition, it shows that the gate dielectric surface treatment not only leads to an increase in mobility in that regime, but also displaces charge transport closer to the interface, hence pointing toward passivation of the charge traps at I/S interface. OFETs with SDS treatment were compared with untreated and vitamin C or hexadecyltrimethylammonium bromide (CTAB) treated OFETs. All the treatments resulted in significant improvements in specific dielectric capacitance, μ_FET, on/off current ratio and transconductance.

As conducting polymer based devices, organic electrochemical transistors (OECTs) are suited for printing process. The convenience of the screen-printing techniques allowed us to design and fabricate OECTs with a selected design and using different gate material. Depending on the material used, we were able to tune the transistor for different biological application. Ag/AgCl gate provided transistor with good transconductance, and electrochemical sensitivity to pH was provided by polyaniline ink. Finally, we validate the enzymatic sensing of glucose and lactate with a Poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) gate often used due to its biocompatible properties. The screen-printing process allowed us to fabricate a large amount of devices in a short period of time, using only commercially available grades of ink, showing by this way the possible transfer to industrial purpose.

Due to their biocompatibility, high transconductance, and low operating voltages, organic electrochemical transistors (OECTs) are promising platforms for biosensing applications. They have been used for measuring enzymes such as glucose and lactate, detecting disruptions of epithelial cell integrity, and amplifying epileptic voltage signals in rat brains. Accelerating the development of OECTs in this diverse range of potential applications, and those unforeseen, requires continued investigation of the device physics and material properties. In this presentation, we will describe our work to better understand OECT behavior, and we will discuss how this understanding can be used to develop more effective biosensors.

We describe ongoing advances toward achieving an integrated all-organic spectrometer on a chip. To this end, 2-dimensional combinatorial arrays of microcavity (μc) organic light emitting diodes (OLEDs) with systematically varying optical cavity lengths were fabricated on a single chip by changing the thickness of different organic and/or spacer layers sandwiched between the two metal electrodes. The latter, one of which is semitransparent, form the cavity. The tunable and narrower emissions from the μcOLEDs serve as excitation sources of varying wavelength for monitoring light absorption or emission. For each wavelength, the light from the μcOLED is partially absorbed by the sample under study and the transmitted light (or the light emitted by an electronically excited sample) is detected by a photodetector (PD). To obtain a compact monitor, an organic PD (OPD) is fabricated and integrated with the μcOLED array. We show the potential of encompassing a broader wavelength range by using μcOLEDs based on different emitting layers. The OPD used to realize the first all-organic integrated spectrometer described here is based on P3HT:PCBM, though more sensitive OPDs we utilized in sensing applications are expected to improve the spectrometers’ performance. The utility of this all-organic μcOLED/OPD spectrometer is shown for monitoring the absorption spectra of P3HT and Alexa Fluor 405 films. The results show excellent agreement with the absorption spectra obtained with a commercial Ocean Optics spectrometer.

Unrepaired DNA damage can lead to mutation, cancer, and death of cells or organisms. However, due to the subtlety of DNA damage, it is difficult to sense the repair of damage products with high selectivity and sensitivity. Here, we show sensitive and selective electrochemical sensing of the repair activity of 8-oxoguanine and uracil glycosylases within DNA monolayers on gold by multiplexed analysis with silicon chips and low-cost electrospun nanofibers. Our approach involves comparing the electrochemical signal of redox probe modified monolayers containing the defect versus the rational control of defect-free monolayers. We find sequence-specific sensitivity thresholds on the order of femtomoles of proteins and dynamic ranges of over two orders of magnitude for each target. For 8-oxoguanine repair, temperature-dependent kinetics are extracted, showing exponential signal loss with time constants of seconds. Electrospun fibers are shown to behave similarly to conventional gold-on-silicon devices, showing the potential of these low-cost devices for sensing applications.

Using a so called pulsetrode concept and two identical ion selective electrodes (ISEs), the concentration of alkali metal ions can be measured without using a reference electrode. This measurement method was demonstrated recently, using all organic ISEs which have been fabricated by simplest means on a plain sheet of paper. Though, this low-cost, all organic ion sensing platform exhibited excellent stability over three months, it required a time consuming conditioning prior to measurement (>1 h). Here, we present a new measurement method which employs a square wave current rather than a single current pulse which is followed by a long regeneration time. This method reduces the conditioning time to 6 minutes, using the same low-cost sensing platform. Furthermore, after the initial conditioning, a quasi continuous measurement is possible. Additionally, using ISEs with different surface areas, a low-cost and simple threshold sensor is demonstrated.

The melanins are a broad class of pigmentary macromolecules found through nature that perform a wide range of functions including photo-protection [1]. The most common melanin – the brown, black pigment eumelanin, has been much studied because of its role in melanoma and also for its functional material properties [2]. Synthetic eumelanin has been shown to be photoconductive in the solid state and also possess a water content dependent dark conductivity [3]. It is now well established that these electrical properties arise from hybrid ionic-electronic behaviour, leading to the proposition that melanins could be model biocompatible systems for ion-to-electron transduction in bioelectronics. In my talk, I will discuss the basic science behind these bioelectronics properties – electrical and optical. In this context I will also describe recent electron paramagnetic spin studies which isolate the role of the various chemical moieties responsible for the hybrid ionic-electronic behaviour. I will also highlight preliminary results on prototype melanin-based bioelectronics devices and discuss possible architectures to realise elements such as solid-state switches and transducers. [1] “The physical and chemical properties of eumelanin”, P. Meredith and T. Sarna, Pigment Cell Research, 19(6), pp572-594 (2006). [2] “Electronic and optoelectronic materials and devices inspired by nature”, P Meredith, C.J. Bettinger, M. Irimia-Vladu, A.B. Mostert and P.E. Schwenn, Reports on Progress in Physics, 76, 034501 (2013). [3] “Is melanin a semiconductor: humidity induced self doping and the electrical conductivity of a biopolymer”, A.B. Mostert, B.J. Powell, F.L. Pratt, G.R. Hanson, T. Sarna, I.R. Gentle and P. Meredith, Proceedings of the National Academy of Sciences of the USA, 109(23), 8943-8947 (2012).

In living systems, protonic and ionic currents are the basis for all information processing. As such, artificial devices based on protonic and ionic currents offer an exciting opportunity for bioelectronics. Proton transport in nature is important for ATP oxidative phosphorylation, the HCVN1 voltage gated proton channel, light activated proton pumping in bacteriorhodopsin, and the proton conducting single water file of the antibiotic gramicidin. In these systems, protons move along hydrogen bond networks formed by water and the hydrated biomolecules (proton wires). We have previously demonstrated complementary H+- and OH-- FETs with acid and base doped biopolymer proton wires and PdHx proton conducting contacts. Here, I will discuss proton-conducting devices based oh highly conductive proton wires that emulate brain synapses, display memristive behaviour, and are connected to form shift registries. Furthermore, I will present the integration of these devices with enzymatic logic gates for integrated biotic-abiotic protonic information processing. Preliminary results on using these devices to affect biological function will be discussed.

In this research, we studied solution-processed non-polymeric organic photodiodes by using the strategy of thick bulk heterojunction (BHJ) and inserting a hole blocking layer to reduce the dark current density. In this system, a high external quantum efficiency (over 70% at -0.5 V), extremely low dark current (0.11 nA/cm² at -0.5 V), and high responsivity (0.4 A/W), detectivity (9.2 x 10¹² Jones), linear dynamic range (140 dB) and frequency response (4.0 MHz) were achieved. This study represents a significant step forward to get a low-cost and high-performance OPDs in a very simple process step.

Fluorescent biomedical markers of today such as dye-infiltrated colloids, microgels and quantum dots suffer from fast bleaching, lack surface functionality (for targets or pharmaceutical agents) and potentially leach heavy metals in case of quantum dots (e.g. Cd). By contrast, conjugated polymer particles are non-cytotoxic, exhibit reduced bleaching, as the entire particle consists of fluorophore, they are hydrophobic and show high quantum yields. Consequently, conjugated polymer particles represent ideal materials for biological applications and imaging. However currently, conjugated polymer particles for biomedical imaging usually lack near-infrared (NIR) emission and are polydisperse. Fluorescent agents with emission in the NIR spectrum are interesting for biomedical applications due to their low photo-damage towards biological species and the ability of NIR radiation to penetrate deep into biological tissue.. I will present the development and synthesis of new conjugated polymers particles with fluorescence in the NIR spectral region for bio-imaging and clinical diagnosis. The particle synthesis proceeds in a one-step Pd or Ni-catalyzed dispersion polymerization of functional NIR emitters. The resulting monodisperse conjugated polymer particles are obtained as a dispersion in a non-hazardous solvent. Different sizes in the sub-micrometer range with a narrow size distribution can be produced. Furthermore biological recognition motifs can be easily attached to the conjugated polymers via thiol-yne click-chemistry providing specific tumor targeting without quenching of the fluorescence. References [1] Kuehne AJC, Gather MC, Sprakel J., Nature Commun. 2012, 3, 1088. [2] Repenko T, Fokong S, De Laporte L, Go D, Kiessling F, Lammers T, Kuehne AJC.,Chem Commun 2015, accepted.

Distributed feedback (DFB) laser sensors with active films consisting of a highly efficient and photostable perylenediimide dye (perylene orange, PDI-O) dispersed in polysytrene (PS), used as passive matrix, are reported. PDIdoped- PS DFB lasers show an excellent operational durability under ambient conditions, superior to those of previously reported DFBs used for sensing purposes. Their bulk refractive index sensing capabilities, under exposure to liquids of different refractive index, have been determined from changes in their emission wavelength. The role of the active film thickness on both, the laser and the sensing performance, has been explored. The use of a thick active film (850 nm) allows obtaining the lowest possible threshold and highest operational lifetime for this type of device although the sensor sensitivity is lower than that achievable with a thin film (160 nm). It is also shown that the inclusion of a high refractive index TiO2 layer on top of the sensor structure allows improving the sensor sensitivity by around two times.

Implantable electrodes are being used for diagnostic purposes, for brain-machine interfaces, and for delivering electrical stimulation to alleviate the symptoms of diseases such as Parkinson’s. The field of organic electronics made available devices with a unique combination of attractive properties, including mixed ionic/electronic conduction, mechanical flexibility, enhanced biocompatibility, and capability for drug delivery. I will present examples of organic electrodes, transistors and other devices for recording and stimulation of brain activity and discuss how they can improve our understanding of brain physiology and pathology, and how they can be used to deliver new therapies.

Regioregular poly(3-hexylthiophene) (rr-P3HT) is suitable for electronic noses and the detection of gaseous biomarkers of human diseases to clinical diagnosis. Nevertheless, thin-film properties such as crystallinity and thickness play a major role in overall device performance. Thin-films were obtained from spin coating of 2–20 mg/mL solutions in chloroform, toluene, chlorobenzene and dichlorobenzene to form a thickness from 20 to 160 nm as measured by atomic force microscopy (AFM). Absorbance spectrum fitted by the sum of three Gaussian curves defined the following parameters, which correlate with the film's electronic structure/morphology: (i) the abscissa at the center of the Gaussian from the highest wavelength, which responds for the P3HT band gap, and (ii) the ratio between the area under the Gaussian centered at the lowest wavelength over the one at the highest wavelength, which corresponds to the amount of amorphous and crystalline phase, respectively. Isosbestic point was determined by thermal annealing temperature variation, while keeping the thickness constant. It was observed that absorbance spectrum shape and, consequently, thin-film morphology depend not only on the concentration of the solution, but also on solvent. Finally, the isosbestic point determined at (470 ± 3) nm provides a linear relationship between absorbance and thickness with y-axis intercept approaching zero. The absorbance spectrum and isosbestic point of P3HT provides a non-destructive, faster and reliable way to estimate thin-film properties as thickness and crystallinity without recurring to AFM and X-ray diffraction (XRD) measurements.