Centre for Energy Research

Monolithic photoelectrodes are a promising way to exploit the excellent optoelectronic properties of organic polymer:non-fullerene bulk-heterojunctions (BHJ) for photoelectrochemical applications. However, the high voltage losses, poor photochemical stability and high synthetic complexity of the most commonly used polymer:non-fullerene combinations have limited their full potential. Here, we address these limitations by introducing a BHJ comprising the low-synthetic-complexity polymer PTQ10 and the near-infrared absorbing acceptor L8-BO. By integrating this new BHJ with a graphite sheet functionalised with a NiFeOOH catalyst, we achieve a low onset potential of +0.64 VRHE, a photocurrent density of 21 mA cm−2 at +1.23 VRHE and a t80 operational stability of 22 h under full AM1.5G illumination in monolithic photoanodes for water oxidation. These values represent a 40 mV increase in photovoltage and a sevenfold improvement in operational stability (t80 extended from 3 h to 22 h) compared to the reference system based on the ternary D18:PM6:L8-BO photoactive blend. Spectroscopic analyses reveal that these improvements stem from the reduced non-radiative voltage losses (from 0.24 V to 0.19 V) and superior photochemical and morphological stability of the PTQ10:L8-BO blend compared to the reference blend. Building on these advances, we demonstrate monolithic tandem photoanodes based on PTQ10:IDIC and PTQ10:L8-BO organic blends, achieving a solar-to-hydrogen efficiency of 6.2%. This work offers critical insights for developing stable, high-efficiency organic photoelectrodes for unassisted solar hydrogen generation.

Ellipsometric mapping measurements and Bayesian evaluation were performed with a non-collimated, imaging ellipsometer using an LCD monitor as a light source. In such a configuration, the polarization state of the illumination and the local angle of incidence vary spatially and spectrally, rendering conventional spectroscopic ellipsometry inversion methods hardly applicable. To address these limitations, a multilayer optical forward model is augmented with instrument-specific correction parameters describing the polarization state of the monitor and the angle-of-incidence map. These parameters are determined through a Bayesian calibration procedure using well-characterized Si-SiO2 reference wafers. The resulting posterior distribution is explored by global optimization based on simulated annealing, yielding a maximum a posteriori estimate, followed by marginalization to quantify uncertainties and parameter correlations. The calibrated correction parameters are subsequently incorporated as informative priors in the Bayesian analysis of unknown samples, including polycrystalline–silicon layers deposited on Si-SiO2 substrates and additional Si-SiO2 wafers outside the calibration set. The approach allows consistent propagation of calibration uncertainties into the inferred layer parameters and provides credible intervals and correlation information that cannot be obtained from conventional least-squares methods. The results demonstrate that, despite the broadband nature of the RGB measurement and the limited number of analyzer orientations, reliable layer thicknesses can be obtained with quantified uncertainties for a wide range of technologically relevant samples. The proposed Bayesian framework enables a transparent interpretation of the measurement accuracy and limitations, providing a robust basis for large-area ellipsometric mapping of multilayer structures.

Abstract Oscillating neural networks are promising candidates for a new computational paradigm, where complex optimization problems are solved by physics itself through the synchronization of coupled oscillating circuits. VO 2 Mott memristors are particularly promising building blocks for such oscillating neural networks. Until now, however, not only the maximum frequency of VO 2 oscillating neural networks, but also the maximum frequency of individual VO 2 oscillators is severely limited, which has restricted their efficient and energy‐saving use. In this study, it is showed how to increase the oscillating frequency by more than an order of magnitude into the 100 MHz range utilizing ultrasmall, ≈30 nm wide active volume VO 2 devices and optimizing the circuit layout for high frequency operation. In addition, the physical limiting factors of the oscillation frequencies are studied by investigating the complex switching dynamics of our nanoscale VO 2 devices. These dynamical studies, together with simulations, provide a clear conclusion on the maximum achievable operating frequencies and the optimal operating parameters under which these can be reached.

Electrical impedance measurements are traditionally macroscopic screening techniques designed to obtain information about the macroscopic internal structure of biological systems. In order to overcome the limitations that the technology detects, mainly with the bulk properties, a miniaturization is employed by developing a complex microfluidic system to achieve cell-scale information. In this work, a microelectrode array was incorporated into a microfluidic chip, allowing localized Electrochemical Impedance Spectroscopy (EIS) measurements, providing impedance data obtained in the spatial and frequency domains simultaneously. The height of the capillary in the microfluidic system was also systematically modified; hence, three types of channels with heights of 10 m, 30 m, and 50 m were developed and studied. The EIS data collection was implemented using two different strategies (two- and four-electrode techniques). Sensitivity analysis was conducted using a microbead solution, where the linear mapping of the number of microbeads along the channel was achieved by EIS. Based on the findings, a complete overview of each measurement implementation was obtained, which is well explained by the physical background presented in the paper. In the case where the capillary height (10 m) is comparable to the diameter of the microbeads (6 m), the four-electrode technique detected the beads in a wider frequency range (approximately between 500 Hz and 50 kHz), while the two-electrode technique detected the beads in a narrower frequency range (approximately between 30 kHz and 300 kHz) with correlation greater than 0.9. In all other cases, a medium (or weak) correlation was found between the impedance data and the longitudinal bead distribution. Based on the results, the technology is ready for further development and adaptation for cell culture purposes.

Fluorescent indicator displacement (FID) assays in which the macrocyclic host is grafted to a graphenic material have the advantage that they operate in turn-on mode, utilizing the FRET-type quenching of the graphenic component. As a contribution to the development of such sensors, we investigated the binding of a cationic and an anionic fluorescent probe, Oxazine 1 and Pyranine (HPTS) to a hybrid nanomaterial rGO-AP6 obtained by attaching a cationic pillar[6]arene (AP6) to reduced graphene oxide (rGO). The solid-state characteristics of this nanomaterial were unveiled using FT-IR, Raman and XP spectroscopy, while its properties in aqueous suspensions were investigated by UV-Vis, fluorescence and Zeta potential measurements. The binding of the two probes was investigated by adsorption studies at pH 6.4 and 10.2, using samples of low concentrations applicable in FID assays. It was found that rGO-AP6 binds HPTS strongly whereas the adsorption of OX is below the detection limit, which is opposite to the trend shown by the unmodified rGO adsorbent. The binding affinity of rGO-AP6 for HPTS could be tuned changing the pH. The AP6 units on the surface of rGO nanosheets proved to be closely homogenous binding sites for this anionic probe. These properties make the supramolecular system HPTS/rGO-AP6 a promising candidate as a fluorescent sensor for appropriate anionic biomolecules like ATP and other nucleotides. In general, the findings of this study underscore the considerable potential of modified rGO nanosheets as platforms for FID sensors. • rGO-AP6 held together by electrostatic interactions of rGO and pillar[6]arene (AP6) • rGO-AP6 adduct functions as a selective adsorbent for anionic HPTS • positive curvature in Stern-Volmer plots of HPTS + rGO-AP6 quencher