Jenny Nelson

The coupling between ionic and electronic species and their dynamic interplay lay the foundation for organic electrochemical transistors (OECTs) to transduce and amplify bio(chemical) signals through ion-modulated conductivity. However, the operation of most reported OECTs is typically dominated by single ions, e.g. anions for p-type accumulation devices, mainly due to the challenge of regulating ion dynamics to enable both types of ions to play a role during the electrochemical doping process. In this study, we propose that electrochemical doping of an OECT channel can occur via an anion-cation dual-doping mechanism, where cation expulsion and anion injection occur simultaneously. By designing a p-type organic mixed ionic-electronic conductor, Pu2gT, with strong side chain-cation interactions, we successfully decelerate the cation transport dynamics, allowing the dual-doping process to occur. As a result, Pu2gT OECT exhibits improved current sensitivity compared with the anion-dominated counterpart, showing potential in high-quality electrocardiogram signal acquisition and ion concentration discrimination. Furthermore, incorporating crown ether additives into Pu2gT enhances the dual-doping effect by further delaying cation dynamics, leading to even higher device performance. This dual-doping mechanism deepens the understanding of OECT working principles and opens avenues for achieving state-of-the-art bioelectronic devices.

PTQ10:L8-BO organic photoactive layers enhance performance and stability of integrated photovoltaic IPV-anodes, delivering 21 mA cm ⁻² , t ₈₀ of 22 h under full solar irradiation (no UV filter), and >6% bias-free STH efficiency in tandem configurations.

Knowledge of the molecular arrangement in the solid state is essential for designing high-performance conjugated polymers. The crystal structures and thermal behavior of their monomers provide important insight into their chain conformation and solid-state structure. Here, single crystals of aromatic thieno[3,2-b]thiophene units bearing mono- to tetraethylene glycol chains, building blocks of some high-performance organic mixed ionic-electronic conductors, are isolated using a robust crystallization protocol and analyzed using single-crystal X-ray diffraction and thermal analysis. Increasing oligoethylene glycol chain length shifts packing from π–π stacking to chain entanglement, accompanied by a melting temperature decrease from 149 to 41 °C. Molecular dynamics simulations using force fields parametrized with density functional theory show greater crystal stability for shorter chains, consistent with stronger π–π interactions relative to chain entanglement. Single crystals of a more extended conjugated system, thiophene-flanked thieno[3,2-b]thiophene with triethylene glycol, show mixed packing motifs and significant disruption of expected S···O interactions, revealing the importance of both side chain and π–π interactions. This work can be anticipated to aid the workup of monomers for synthesis, clarify packing motifs that govern structure–property relationships in conjugated polymers, and enable force-field implementation to guide organic semiconductor design and deepen understanding of their microstructure.

Through remarkable advances in materials design, the efficiency of photovoltaic energy conversion in molecular materials has risen from 1% to over 20% within 2 decades. Some recent reports argue that charge photogeneration can occur directly in neat films of the best-performing molecular materials, and that this process may assist current generation in heterojunction devices. Here we address this assertion by combining experimental measurements of charge generation in single-component and heterojunction devices with a computational model of the generation and evolution of delocalized excited states in such systems. We identify key molecular parameters that are likely to assist charge generation in high-performance materials, including the exciton binding energy, reorganization energy, energetic disorder, electronic coupling and the molecular packing motif. We show that including state delocalization is critical to the results. While we find that charge generation in single domains is unlikely to drive photocurrent generation in low-offset heterojunctions, the same molecular parameters favour charge generation in both device architectures.

Agrivoltaic systems offer the potential to boost land productivity, reduce water consumption and improve access to energy: an energy-food-water nexus solution. Agrivoltaic systems are promising for regions with relatively low land productivity and both energy- and water-access challenges, such as sub-Saharan Africa. However, there is a lack of research exploring the use of agrivoltaics in such contexts. This study addresses that gap. It uses both energy-system and crop modelling to explore optimal agrivoltaic system design and deployment for a medium-sized farm, located in Zimbabwe, where electricity is expensive and unreliable. We compare conventional, ground-mounted PV mini-grid systems with three agrivoltaic system configurations. We model fixed-tilt, single-axis tracking and vertical bifacial configurations installed above wheat and maize. We calculate the optimal required system sizes at 100% and 95% reliability levels. We find that the cheapest agrivoltaic system (on a unit cost basis) is single-axis tracking, with a unit cost only 11% higher than the ground-mounted PV at an equivalent 95% reliability level. Under our base-case scenario, high electricity costs from the grid mean that the farm is operating with a deficit (when considering crop revenues). However, with agrivoltaic systems, the deficit is significantly reduced and at 95% reliability, the farm becomes profitable with crop revenue exceeding upkeep costs. Of the agrivoltaic systems, all were profitable though this varied depending on the ratio between module spacing and height (P-by-H ratio). We found greater system profitability at higher P-by-H ratios, with the largest improvement when switching from a P-by-H ratio of 2 to 3. All agrivoltaic system types can achieve land-equivalent ratios (LERs) greater than 1, depending on the P-by-H ratio, indicating improved efficiency. Our calculation of the price-performance ratio (PPR) found that all system types were economical.

Using ultrafast time-resolved infrared (TRIR) spectroscopy, we studied the solution-phase excited-state structural evolution of an indacenodithiophene-co-benzothiadiazole polymer (C8-IDTBT). Following band gap excitation, the TRIR spectra reveal vibrational features that develop within 10 ps and decay over 4 ns. Using pulse radiolysis measurements, charge-modulation spectroscopy, and quantum-chemical calculations, the IR features are assigned to polaron pairs. Interestingly, these features appear on an evolving broad mid-IR electronic absorption background, with kinetics correlating with the formation and decay of the cation-radical vibrational bands. A three-state kinetic model successfully reproduces the spectral evolution, revealing that the polaron and exciton populations exist in dynamic equilibrium on picosecond time scales, with time constants for exciton dissociation in the range of 3-5 ps and polaron-to-exciton reformation between 20 and 100 ps, while both species decay to the ground state on much slower nanosecond time scales (∼1 ns), yielding a remarkably high polaron-generation efficiency, higher than 50%. These findings provide fundamental insights into intramolecular charge photogeneration mechanisms in conjugated polymers, demonstrating efficient bound-polaron formation in isolated polymer chains.

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.

Computationally expensive periodic DFT calculations are not necessary to screen the electronic properties of molecular crystals for photocatalytic water splitting, as fast single-molecule calculations are shown to provide similar accuracy.

The discovery of chlorophyll f–containing photosystems, with their long-wavelength photochemistry, represented a distinct, low-energy paradigm for oxygenic photosynthesis. Structural studies on chlorophyll f–containing photosystem I could identify some chlorophyll f sites, but none among the photochemically active pigments, and thus concluded that chlorophyll f plays no photochemical role. Here, we report two cryo–electron microscopy structures of far-red photosystem I from Chroococcidiopsis thermalis PCC 7203, allowing the assignment of eight chlorophyll f molecules, including the redox active A _−1B . Simulations of absorption difference spectra induced by charge separation indicated that the experimental spectra can be reproduced only by considering the presence of a chlorophyll f at the A _−1B site. The chlorophyll f locations, wavelength assignments, and conserved far-red–specific residues provide functional insights for efficient use of long-wavelength photons.