Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm−1, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion mode of operation. BBL:PEI inks hold promise for the development of next-generation bioelectronics and wearable devices, in particular targeting novel functionality, efficiency, and power performance.

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Harnessing solar energy for the production of clean hydrogen by photo­electrochemical water splitting represents a very attractive, but challenging approach for sustainable energy generation. In this regard, the fabrication of Fe2O3–TiO2 photoanodes is reported, showing attractive performances [≈2.0 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode in 1 M NaOH] under simulated one‐sun illumination. This goal, corresponding to a tenfold photoactivity enhancement with respect to bare Fe2O3, is achieved by atomic layer deposition of TiO2 over hematite (α‐Fe2O3) nanostructures fabricated by plasma enhanced‐chemical vapor deposition and final annealing at 650 °C. The adopted approach enables an intimate Fe2O3–TiO2 coupling, resulting in an electronic interplay at the Fe2O3/TiO2 interface. The reasons for the photocurrent enhancement determined by TiO2 overlayers with increasing thickness are unraveled by a detailed chemico‐physical investigation, as well as by the study of photo­generated charge carrier dynamics. Transient absorption spectroscopy shows that the increased photoelectrochemical response of heterostructured photoanodes compared to bare hematite is due to an enhanced separation of photogenerated charge carriers and more favorable hole dynamics for water oxidation. The stable responses obtained even in simulated seawater provides a feasible route in view of the eventual large‐scale generation of renewable energy.

Harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen is receiving increasing attention in the search of alternative energy resources. In this regard, hematite (α-Fe2O3) nanostructures with controlled nano-organization have been fabricated and investigated for use as anodes in photoelectrochemical (PEC) cells. The target systems have been grown on conductive substrates by plasma enhanced-chemical vapor deposition (PE-CVD) and subjected to eventual ex situ annealing in air to further tailor their structure and properties. A detailed multitechnique approach has enabled to elucidate the interrelations between system characteristics and the generated photocurrent. The present α-Fe2O3 systems are characterized by a high purity and hierarchical morphologies consisting of nanopyramids/organized dendrites, offering a high contact area with the electrolyte. PEC data reveal a dramatic response enhancement upon thermal treatment, related to a more efficient electron transfer. The reasons underlying such a phenomenon are elucidated and discussed by transient absorption spectroscopy (TAS) studies of photogenerated charge carrier kinetics, investigated on different time scales for the first time on PE-CVD Fe2O3 nanostructures.

We investigated the impact of Singly Occupied Molecular Orbital (SOMO) energy on the n-doping efficiency of benzimidazole-derivatives. By designing and synthesizing a series of new air-stable benzimidazole-based dopants with different SOMO energy levels, we demonstrated that an increase of the dopant SOMO energy by only ~0.3 eV enhances the electrical conductivity of a benchmark electron-transporting naphthalenediimide-bithiophene polymer by more than one order of magnitude. By combining electrical, X-ray diffraction, and electron paramagnetic resonance measurements with density functional theory calculations and analytical transport simulations, we quantitatively characterized the conductivity, Seebeck coefficient, spin density, crystallinity of the doped polymer as a function of the dopant SOMO energy. Our findings strongly indicate that charge and energy transport are dominated by the (relative) position of the SOMO level, whereas morphological differences appear to play a lesser role. These results set molecular-design guidelines for next-generation ntype dopants.

scaling law, states that the supply voltage for each new CMOS generation is reduced by 30%, and the power consumption subsequentially reduces by 50%. After decades of development, the latest 7-nm-node CMOS process reaches a supply voltage of 0.75 V. [2] Today, the Si-CMOS technology is heavily explored in Internet of Things (IoT) applications, serving as low-power outposts that record physical sensor parameters (e.g., motion, light, temperature), communicate over long distances, and harvest and store energy for its operation. [3] Expanding IoT modules with flexible, soft, or large-area chemical sensors and actuators only possible off-Si, enables a circuit technology that can amplify and route signals, facilitating signal compatibility and low-cost integration between Si-technology and embedded devices. Further, for many IoT and bioelectronic applications (e.g., (bio-)chemical sensors and neuronal interfacing), the on-site technology is preferably realized without Sichips to enable many different form factors, proximity, elasticity, and signal transduction, tailor-made for the actual chemical/biological environment. Also in this case, a low-power/voltage, high-performing, and flexible circuit technology operating at the site of stimulation or sensing is needed to record and transfer signals at high signal-to-noise performance. The ability to accurately extract low-amplitude voltage signals is crucial inseveral fields, ranging from single-use diagnostics and medical technology to robotics and the Internet of Things (IoT). The organic electrochemical transistor (OECT), which features large transconductance values at low operating voltages, is ideal for monitoring small signals. Here, low-power and high-gain flexible circuits based on printed complementary OECTs are reported. This work leverages the low threshold voltage of both p-type and n-type enhancement-mode OECTs to develop complementary voltage amplifiers that can sense voltages as low as 100 µV, with gains of 30.4 dB and at a power consumption of 0.1-2.7 µW (single-stage amplifier). At the optimal operating conditions, the voltage gain normalized to power consumption reaches 169 dB µW −1 , which is >50 times larger than state-of-the-art OECTbased amplifiers. In a monolithically integrated two-stage configuration, these complementary voltage amplifiers reach voltage gains of 193 V/V, which are among the highest for emerging complementary metal-oxide-semiconductorlike technologies operating at supply voltages below 1 V. These flexible complementary circuits based on printed OECTs define a new power-efficient platform for sensing and amplifying low-amplitude voltage signals in several emerging beyond-silicon applications.

Doping of organic semiconductors is a powerful tool to optimize the performance of various organic (opto)­electronic and bioelectronic devices. Despite recent advances, the low thermal stability of the electronic properties of doped polymers still represents a significant obstacle to implementing these materials into practical applications. Hence, the development of conducting doped polymers with excellent long-term stability at elevated temperatures is highly desirable. Here, we report on the sequential doping of the ladder-type polymer poly­(benzimidazobenzophenanthroline) (BBL) with a benzimidazole-based dopant (i.e., N-DMBI). By combining electrical, UV–vis/infrared, X-ray diffraction, and electron paramagnetic resonance measurements, we quantitatively characterized the conductivity, Seebeck coefficient, spin density, and microstructure of the sequentially doped polymer films as a function of the thermal annealing temperature. Importantly, we observed that the electrical conductivity of N-DMBI-doped BBL remains unchanged even after 20 h of heating at 190 °C. This finding is remarkable and of particular interest for organic thermoelectrics.

Abstract