Organic mixed ionic/electronic conductors (OMIECs) have gained considerable interest in bioelectronics, power electronics, circuits and neuromorphic computing. These organic, often polymer-based, semiconductors rely on a combination of ionic transport, electronic transport, and high volumetric charge storage capacity. Bulk transport properties of OMIECs enable organic electrochemical transistor (OECT) device concepts that achieve co-localization of sensing with signal processing, including amplification of electrophysiological signals and devices with highly non-linear responses for spiking neurons. Furthermore, we report on OECT implementation that result in a three to four order-of-magnitude sensitivity enhancement in electrochemical aptamer-based biochemical sensors.

In recent years, immense efforts in the flexible electronics field have led to unprecedented progress and to devices of ever increasing performance. Despite these advances, new opportunities are sought in order to widen the applications of organic-based technologies and expand their functionalities and features. We discuss here challenges and opportunities, with focus on the use of multicomponent systems for, e.g., increasing the mechanical flexibility and stability of organic electronic products, or introducing other features such as self-encapsulation and faster mixed ion-electron transport. One specific strategy is based on blending polymeric insulators with organic semiconductors; which has led to a desired improvement of the mechanical properties of organic devices, producing in certain scenarios robust and stable architectures. Here we discuss the working principle of semiconductor:insulator blends, examining the different approaches that have recently been reported in literature. We illustrate how organic field-effect transistors (OFET)s and organic solar cells (OPV)s can be fabricated with such systems without detrimental effects on the resulting device characteristics even at high contents of the insulator. Furthermore, we review how blending can assist in the fabrication of more reliable and versatile organic electrochemical transistors (OECT)s.

Organic semiconductors, derived from π-conjugated molecules and polymers, offer significant potential for (opto)electronics applications with finely tuned electronic, optical, and mechanical properties. While chemists have the capacity to manipulate molecular-scale electronic, redox, and optical properties that in turn determine organic semiconductor response, the chemical design space for organic semiconductors is vast, and it is not clear that current Edisonian practices of make, test, and repeat offer the ability to identify systems as efficiently as required for many needed technology advances. Here we will discuss the development of the OCELOT (Organic Crystals for Electronic and Light Oriented Technologies) data infrastructure for the collection and dissemination of experimental and computational data for π-conjugated molecules and organic semiconductors, developed under the auspices of the FAIR data principles with the aim that all data and models are AI (artificial intelligence)-ready. Among the data tools offered on OCELOT, we will discuss the development of machine-learning models to predict molecular and semiconductor electronic, redox, and optical properties.

The true structure of alternating conjugated polymers – the state-of-the-art materials for a number of organic electronics technologies – often deviates from the idealized picture but this gets relatively limited attention. Here, we quantify the amount of homocoupling defects resulting from Stille polymerization and shed new light on the actual distribution of these structural defects in a prototype polymer material. Further, when compared to a homocoupling-free variant, these defects hinder fullerene intercalation, with a clear implication on charge-transfer absorption. This demonstrates that molecular defects may (strongly) impact polymer and blend properties and calls for increased attention for defect-free materials.

Combining electrospray (ESD) and scanning tunnelling microscopy (STM) has shown in recent years to reliably grant access to individual polymer strands within self-assembled polymer monolayers with submolecular resolution. Here, this methodology is used to study the microstructural properties that influence intra- and inter-chain charge transport in the case of the amorphous polymer IDT-BT. The analysis of STM images allows us to precisely determine backbone conformations and statistically infer torsional potential energies for IDT-BT, to quantify the size and relative orientation of nanoaggregates within the polymer monolayers, and to provide the exact geometrical configuration of short-contact crossing points between polymer backbones.

In my talk, I will discuss the importance of microstructure and dynamic microstructural rearrangements of OMIECs that greatly influence the electronic charge transport properties in electrochemical transistors. I will discuss new chemical design strategies OMIECs to utilize these findings to improve the performance of OMIECs in electrochemical transistors.

The emerging research field of organic bioelectronics has developed rapidly over the last few years and elegant examples of biomedically important applications including for example in-vivo drug delivery and neural interfacing have been demonstrated. The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous environment, is an ideal device to utilise in bioelectronic applications. Initially, nearly all OECTs were fabricated with commercially available PEDOT:PSS, heavily limiting the variability in performance. We have previously shown that tailor-made semiconducting polymers are fully capable of matching the performance of PEDOT:PSS and over the last few years the library of mixed ionic-electronic conductors for OECT applications have expanded significantly. To capitalise on this development and the versatility of the organic chemistry toolbox, further materials development is needed. In my talk I will discuss our recent work in this area covering examples of both molecular and polymeric semiconducting materials and their performance in organic electrochemical transistors.

The development of organic electrochemical transistors (OECTs) capable of maintaining their high amplification, fast transient speed, and operational stability in harsh environments will advance the growth of next‐generation wearable electronics, robotics and biological electronics. In this study, a high-performance solid-state OECT (SSOECT) is successfully demonstrated, showing a recorded high transconductance of 220 ± 59 S cm−1, ultrafast device speed of ≈10 kHz with excellent operational stability over 10 000 switching cycles, and thermally stable under a wide temperature range from −50 to 110 °C. The developed SSOECTs are successfully used to detect low-amplitude physiological signals, showing a high signal-to-noise-ratio of 32.5 ± 2.1 dB. For the first time, the amplifying power of these SSOECTs is also retained and reliably shown to collect high-quality electrophysiological signals even under harsh temperatures. The demonstration of high-performing SSOECTs and its application in harsh environment are core steps toward their implementation in next-generation wearable electronics and bioelectronics. We also will present our recent work on developing fibrous electrolyte containing polymer matrix and ionic liquid, which is highly robust, breathable, waterproof, and conformal with human skin is reported. Serving as fibrous substrate and electrolyte of OECTs, a high transconductance of ≈0.8 mS, stability over pulsing and time (≈1000 cycles and 30 days) are achieved. The softness of fibrous OECTs enables a comfortable contact after attaching to human skin, which can reduce the interfacial impedance to achieve a high-quality local amplification of the electrocardiography signals (signal-to-noise ratio of 21.7 dB) even in skin squeezed state or after one week. These results indicated that our fibrous OECTs have huge potential for versatile on-skin electronics such as non-invasive medical monitoring, soft sensors, and textile electronics.

This talk presents our recent advances in flexible and printed integrated circuits and biosensor arrays. First, the vertical stacking of three complementary transistors is introduced to design and fabricate 3D active-matrix multi-sensor arrays, which can independently measure temperature and pressure in real time. Second, inkjet-printed organic voltage amplifiers are presented by monolithically integrating organic electrochemical transistors (OECT) and thin-film polymer resistors on a single, highly flexible substrate for in vivo brain activity recording. Finally, a 3D tissue-integrated ion sensing platform based on OECTs is presented. We inkjet-printed large-area OECTs and integrated them with 3D-bioprinted lung models for the first time.

Metal halide perovskites are promising alternatives to organic semiconductors and metal oxides for printed electronic applications. Their facile processability allows them to be fabricated through a wide variety of techniques. However there are multiple challenges that halide perovskite transistors need to manage before they are strong contenders. The primary problem associated with halide perovskites are the ionic migration effects which limit room temperature operation. TFT operation at room temperature is primarily achieved via precise compositional, microstructural control or via surface/substrate/electrode treatments. Here, tin doped indium oxide is utilized as source/drain contacts to fabricate a room temperature operational n-type solution-processed Cs(MAFA)Pb(BrI) transistor. Moreover we demonstrate optical learning in these TFTs by exploiting the photoactive nature and gate bias effects of this transistor.

In this presentation, I will discuss advancements in monolayer organic transistors using C10-DNTT. We can directly achieve large, crystallized C10-DNTT areas on silicon substrates, but compatibility with traditional methods is limited. I'll explain the principles of electrode transfer and semiconductor patterning stamps for fabricating OFETs with 2µm channel lengths without chemicals or damage. We integrated the monolayer OFET into an AC/DC rectifying circuit, achieving a 17.3 MHz cutoff frequency.

In addition to optimizing the charge carrier mobility (μ) in organic semiconductor devices, it is critical to improve operational stability. We investigated organic field-effect transistors (OFETs) made from several conjugated polymers based on indacenodithiazole (IDTz). Surface treatment of the electrode enabled us to tune the transport from p-type to n-type, while thermal annealing improved μ to 1.35 cm2/Vs. We bias-stressed the OFETs for about 24h hours at constant DC conditions (VGS= VDS= 60V) and found that in the most optimized devices only minor changes in the properties occur, i.e. 3% decrease in mobility and threshold voltage shift of maximum 2V.

Organic phototransistors (OPTs) are promising flexible photodetectors, but it is challenging to achieve high photosensitivity due to their intrinsic on-state current regardless of lighting conditions. In this study, photomultiplication-type organic phototransistors (PM-OPTs) are developed to suppress a dark current while producing a large photocurrent. A thin blocking layer is inserted between the source/drain electrodes and the active layer to induce a photomultiplication effect. The proposed PM-OPTs show two orders of magnitude larger photosensitivity whereas 100 times less power consumption in dark compared to conventional OPTs. We believe the proposed devices are suitable for realizing accurate and energy-efficient wearable bio-signal sensors.

Charge transport in organic small molecule transistors is strongly connected to the crystal packing of the organic material. Our approach to inducing favorable orientations in organic small molecule systems is evolving, and we are developing new approaches to device enhancement through manipulating the degrees of freedom in both the chromophore and the peripheral solubilizing groups. More recently, we have explored the modification of our materials to move beyond pure charge transport issues, to improve the sensitivity of transistor-based sensors. Here, we will discuss our new observations of improved supramolecular synthons for dense and ordered crystal packing, atomic modifications to improve sensor performance, and rigidification of the entire molecular system to minimize the impact of dynamic motions. I will then discuss briefly the application of these design principles to the development of new molecules for use in organic electrochemical transistors.

Field-effect transistors (FETs) provide an ideal and versatile platform to study electronic properties of perovskite semiconductors. However, the fabrication of reliable perovskite FETs has remained an enormous challenge due to the severe ion migration, which can screen the applied gate electric field, resulting in poor device performance. Two-dimensional (2D) perovskites with bulky spacer cations are promising candidates for FET application due to the suppressed ion movement by large size insulating ligands. Unfortunately, to date, most research on organic cations is based on trial-and-error tests by picking the spacers randomly to incorporate into layered perovskites and devices. The correlation between chemical nature of the organic cations, film morphology, crystallinity, molecular organization, and charge carrier transport in 2D layered perovskites is still not well understood, thus, significantly limiting the development of 2D perovskite FETs. In this report, we selected five different lengths of the linear alkyl ammonium organic cation to incorporate in 2D Sn-based perovskites. It is found that the chain length of the cation spacer and the film processing parameters significantly influence the film morphology and crystal orientation, which in turn affect local charge carrier mobility, as confirmed by terahertz spectroscopy, and finally determine the charge carrier transport in FET devices. Additionally, temperature-dependent charge transport measurements reveal a switch from negative mobility coefficient dominated by ion migration to a thermally activated regime with positive coefficient with increasing temperature. Such transport behaviour has not been observed so far for 2D layered perovskite FETs. We believe this work provides a general guideline on rational design principles of organic spacer cations in 2D perovskite for FET applications.

We study the macroscopic and microscopic conductivity of doped polythiophenes and vary the electrostatic environment with polar side chains or anion exchange of the dopant. Optimized doping of P3HT with a strong oxidant and anion exchange increases the conductivity to up to 190 S/cm mainly by increasing the number of contributing charges. Furthermore, oligo ethylene glycol side chains increase the conductivity to up to 750 S/cm by increasing (i) the number of contributing charges and (ii) also their mobility in comparison to P3HT with alkyl side chains. We dynamically investigate the spectral changes in absorbance during chemical doping and correlate the conductivity to an ideal ratio between polarons and bipolarons. Understanding the macroscopic and microscopic conductivity as well as the doping dynamics are keys for designing efficient transistors based on doped organic semiconductors.

Organic semiconductors are multifunctional soft electronic materials that play an impactful role in the flexible electronics industry. Their use spans printed electronic circuits, large area displays, flexible solar energy harvesters, and implantable bioelectronics. For their competitive optical, electronic, thermoelectric, and spin-based properties, these soft electronic materials attract significant academic engagement, seeding new technologies for the future. [1, 2, 3] Although macroscopic flexibility on the centimetre to metre scale is a unique selling point for organic semiconductor technology, not much is known about their mechanical properties on the nanoscale. Quantification of these nanomechanical properties, and an understanding of nanoscale stiffness tunability and nanoscale homogenisation, holds significant potential for fundamental and applied science. [4, 5] During the last decade, the development of high precision atomic force microscopes has made it possible to quantify the mechanical properties of organic polymers on the scale of a few polymer chains. Techniques such as higher eigen mode imaging make it possible to visualise molecular ordering on the nanoscale under ambient conditions with ease. These techniques allow one to correlate molecular ordering with the stiffness that such ordering manifests. In this talk, the science and technology of precision nanoscale measurement of mechanics will be spotlight. The interrelation between molecular organisation and nanomechanical properties in high-performance polymers used for organic electronics will be shown. [6, 7] A quantification of differences in strain within organic nanocrystal polymorphs will also be demonstrated. The measurement techniques demonstrated in this talk are extendable to a wide variety of multifunctional materials with a broad range of elastic properties and have significant use in both academia and industry. References [1] D. Venkateshvaran, M. Nikolka et al., Nature 515, 384–388 (2014) [2] S. J. Wang, D. Venkateshvaran et al., Nature Electronics 2, 98–107 (2019) [3] P. Skalski, O. Zadvorna et al., Physical Review Materials 6, 024601 (2021) [4] L. Ouyang, C. Kuo et al., J. Mater. Chem. B 3, 5010 (2015) [5] C. D. Gerardo et al., Microsystems and Nanoengineering 4, 19 (2018) [6] V. Panchal, I. Dobryden … D. Venkateshvaran, Advanced Electronic Materials 8, 2101019 (2022) [7] I. Dobryden, V. V. Korolkov … D. Venkateshvaran, Nature Communications 13, 3076 (2022)

Electric field induced second harmonic generation (EFISHG) techniques accurately map the electric field in the channel of a thin film transistor and provide insights into mobile charge distribution as well as interface and bulk trapped charge distribution in the semiconductor and dielectric layers. Since the method is sensitive to both mobile and trapped charges, it is valuable for monitoring carrier dynamics in organic field-effect transistors (FETs). Time-resolved EFISHG images from organic FETs yield real-time motion of the carrier dynamics, providing an alternate estimate of contact-free and trap-free carrier mobility.

Organic infrared photodetectors with improved detectivity would enable low-cost spectroscopic analysis and other imaging applications. However, organic infrared materials are challenged by inefficient transduction due to increasing recombination with lower bandgaps. Here we report the approach of phototransistor structures to increase signal gain for materials responsive from 1100 to 1800 nm with a peak absorption of 1550 nm. The device is consisted of a bilayer transistor channel that decouples charge photogeneration and transport, enabling charge injection for signal gain. The frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions. Lastly, we will also compare the phototransistor performance to a metal-insulator-semiconductor capacitive detector, to evaluate the potentials and tradeoff for these alternative structures for infrared detection.