Solution processable organic semiconductors are well‐established as high‐performance materials for inexpensive and scalable solar energy conversion in organic photovoltaic (OPV) devices, but their ...promise in the economic conversion of solar energy into chemical energy (solar fuels) has only recently been recognized. Herein, the main approaches employing organic semiconductor‐based devices toward solar H2 generation via water splitting are compared and performance demonstrations are reviewed. OPV‐biased water electrolysis is seen to advance significantly with the development of the tandem OPV device and the optimization of operating potential and redox catalysts. This approach now exceeds 6% solar‐to‐hydrogen conversion efficiency while over 10% is reasonably feasible. By contrast, while the direct water splitting by an organic semiconductor in a photo‐electrochemical cell has attractive advantages, increasing the performance remains a challenge. Photocathodes employing a bulk‐heterojunction have been optimized to give 7–8 mA cm−2 water reduction photocurrent under standard conditions, but photoanodes remain <1 mA cm−2, and robustness remains a critical issue. However, recent investigations into the direct organic semiconductor/electrolyte interface have brought important insights into free charge generation, the nature of the semiconductor/catalyst interface, and the stability of organic photoelectrodes. Outlooks toward advancing both approaches are discussed.
Splitting water with sunlight and organic semiconductor devices is emerging as a promising approach for the inexpensive and scalable solar fuel production. Herein, organic semiconductor based devices for solar water splitting are systematically reviewed. The challenges facing the advance of both photovoltaic‐based electrolysis and photo‐electrochemical cells are highlighted while new directions to consolidate these technologies are proposed.
Developing tools to understand and control the effect of semiconducting polymer morphology on the optoelectronic performance remains an important objective. Introducing conjugation break spacers ...(i.e., flexible linkers) between π-conjugated segments in a semiconducting polymer is an emerging strategy toward this goal. Herein, we place this strategy in context with other extrinsic and intrinsic engineering approaches and highlight some of the recent results employing this “flexible linker” approach. We see that the inclusion of electrically insulating aliphatic spacers represents a versatile tool to gain insight into the nature of inter-molecular and intra-molecular charge carrier transport and can be broadly used to control morphology of solution-processed semiconducting polymer thin films. Moreover, this approach has afforded unique control over material processing and mechanical properties (e.g., viscosity and elasticity) without detrimental effect on the semiconducting ability. While the development of this technique remains at an early stage, its potential gives promise to reaching the goal of engineering the self-assembly of semiconducting polymers.
Solution-processable semiconducting polymers have been explored over the last decades for their potential applications in inexpensively fabricated transistors, diodes and photovoltaic cells. However, ...a remaining challenge in the field is to control the solid-state self-assembly of polymer chains in thin films devices, as the aspects of (semi)crystallinity, grain boundaries, and chain entanglement can drastically affect intra-and inter-molecular charge transport/transfer and thus device performance. In this short review we examine how the aspects of molecular weight and chain rigidity affect solid-state self-assembly and highlight molecular engineering strategies to tune thin film morphology. Side chain engineering, flexibly linking conjugation segments, and block co-polymer strategies are specifically discussed with respect to their effect on field effect charge carrier mobility in transistors and power conversion efficiency in solar cells. Example systems are taken from recent literature including work from our laboratories to illustrate the potential of molecular engineering semiconducting polymers.
Understanding body malodour in a measurable manner is essential for developing personal care products. Body malodour is the result of bodily secretion of a highly complex mixture of volatile organic ...compounds. Current body malodour measurement methods are manual, time consuming and costly, requiring an expert panel of assessors to assign a malodour score to each human test subject. This article proposes a technology-based solution to automate this task by developing a custom-designed malodour score classification system comprising an electronic nose sensor array, a sensor readout interface and a machine learning hardware fabricated on low-cost flexible substrates. The proposed flexible integrated smart system is to augment the expert panel by acting like a panel assessor but could ultimately replace the panel to reduce the test and measurement costs. We demonstrate that it can classify malodour scores as good as or even better than half of the assessors on the expert panel.
A modular approach to underexplored, unsymmetrical 1benzothieno3,2-
b
1benzothiophene (BTBT) scaffolds delivers a library of BTBT materials from readily available coupling partners by combining a ...transition-metal free Pummerer CH-CH-type cross-coupling and a Newman-Kwart reaction. This effective approach to unsymmetrical BTBT materials has allowed their properties to be studied. In particular, tuning the functional groups on the BTBT scaffold allows the solid-state assembly and molecular orbital energy levels to be modulated. Investigation of the charge transport properties of BTBT-containing small-molecule:polymer blends revealed the importance of molecular ordering during phase segregation and matching the highest occupied molecular orbital energy level with that of the semiconducting polymer binder, polyindacenodithiophene-benzothiadiazole (PIDTBT). The hole mobilities extracted from transistors fabricated using blends of PIDTBT with phenyl or methoxy functionalized unsymmetrical BTBTs were double those measured for devices fabricated using pristine PIDTBT. This study underscores the value of the synthetic methodology in providing a platform from which to study structure-property relationships in an underrepresented family of unsymmetrical BTBT molecular semiconductors.
A modular approach to underexplored, unsymmetrical 1benzothieno3,2-
b
1benzothiophene (BTBT) scaffolds, combining a transition-metal free Pummerer CH-CH-type cross-coupling and a Newman-Kwart reaction, delivers a library of BTBT materials.
Organic semiconductors (OSCs) promise to deliver next‐generation electronic and energy devices that are flexible, scalable and printable. Unfortunately, realizing this opportunity is hampered by ...increasing concerns about the use of volatile organic compounds (VOCs), particularly toxic halogenated solvents that are detrimental to the environment and human health. Here, a cradle‐to‐grave process is reported to achieve high performance p‐ and n‐type OSC devices based on indacenodithiophene and diketopyrrolopyrrole semiconducting polymers that utilizes aqueous‐processes, fewer steps, lower reaction temperatures, a significant reduction in VOCs (>99%) and avoids all halogenated solvents. The process involves an aqueous mini‐emulsion polymerization that generates a surfactant‐stabilized aqueous dispersion of OSC nanoparticles at sufficient concentration to permit direct aqueous processing into thin films for use in organic field‐effect transistors. Promisingly, the performance of these devices is comparable to those prepared using conventional synthesis and processing procedures optimized for large amounts of VOCs and halogenated solvents. Ultimately, the holistic approach reported addresses the environmental issues and enables a viable guideline for the delivery of future OSC devices using only aqueous media for synthesis, purification and thin‐film processing.
An environmentally benign cradle‐to‐grave process from synthesis‐to‐device is demonstrated for high performance organic field‐effect transistors. This holistic approach uses aqueous processes from mini‐emulsion polymerization to purification and thin‐film deposition. Compared to conventional approaches, the process requires fewer steps, lower reaction temperatures, a significant reduction in the use of volatile organic compounds and avoids toxic halogenated solvents.
Exfoliated transition metal dichalcogenides (2D-TMDs) are attractive light-harvesting materials for large-area and inexpensive solar energy conversion given their ability to form highly tolerant ...heterojunctions. However, the preparation of large-area heterojunctions with these materials remains a challenge toward practical devices, and the details of photogenerated charge carrier harvesting are not well established. In this work, we use all solution-based methods to prepare large-area hybrid heterojunction films consisting of exfoliated semiconducting 2H-MoS2 flakes and a perylene-diimide (PDI) derivative. Hybrid photoelectrodes exhibited a 6-fold improvement in photocurrent compared to that of bare MoS2 or PDI films. Kelvin probe force microscopy, X-ray photoelectron spectroscopy, and transient absorption measurements of the hybrid films indicate the formation of an interfacial dipole at the MoS2/organic interface and suggest that the photogenerated holes transfer from MoS2 to the PDI. Moreover, performing the same analysis on MoSe2-based hybrid devices confirms the importance of proper valence band alignment for efficient charge transfer and photogenerated carrier collection in TMD/organic semiconductor hybrid heterojunctions.
Next-generation wearables will interface intimately with the human body either on-skin, implanted or woven into clothing. This requires electrical components that match the mechanical properties of ...biological tissues stretchability (up to 60% strain) and softness (Young's modulus of 1 kPa to 1 MPa). As wearables become increasingly complex, the energy and mechanical requirements will increase, and an integrated power supply unit such as a soft and stretchable battery is needed to achieve autonomy and wireless operation. However, two key challenges remain for current stretchable battery technology: the mechanical performance (softness and stretchability) and its relation to the size and charge storage capacity (challenge I), and the sustainability and biocompatibility of the battery materials and its components (challenge II). Integrating all these factors into the battery design often leads to a trade-off between the various properties. This perspective will evaluate current strategies for achieving sustainable stretchable batteries and provide a discussion on possible avenues for future research.
Stretchable battery technology still faces several challenges to progress the development of next-generation wearables. This perspective will evaluate current strategies and provide a discussion on possible avenues for future research.
A novel class of light‐responsive π‐conjugated compounds incorporates photochromic torsional switches (PTS). These compounds are able to tune the planarization of their π‐conjugated backbone, and ...thus their optical and electronic properties, by using light as an external stimulus. The PTS unit is based on a bithiophene fragment linked to a photochromic azobenzene moiety. When this PTS‐containing oligothiophene is not exposed to light, the azobenzene moiety assumes its extended trans conformation, which forces the oligothiophene backbone to twist out of coplanarity. Exposure to UV light results in isomerization to the cis conformation, which allows the bithiophene fragment to assume a planar, π‐conjugated conformation. More information can be found in the Research Article by D. Fazzi, E. Orentas, G. Sforazzini, and co‐workers (DOI: 10.1002/chem.202202698).
A wide range of nanophotonic applications rely on polarization‐dependent plasmonic resonances, which usually requires metallic nanostructures that have anisotropic shape. This work demonstrates ...polarization‐dependent plasmonic resonances instead by breaking symmetry via material permittivity. The study shows that molecular alignment of a conducting polymer can lead to a material with polarization‐dependent plasma frequency and corresponding in‐plane hyperbolic permittivity region. This result is not expected based only on anisotropic charge mobility but implies that also the effective mass of the charge carriers becomes anisotropic upon polymer alignment. This unique feature is used to demonstrate circularly symmetric nanoantennas that provide different plasmonic resonances parallel and perpendicular to the alignment direction. The nanoantennas are further tuneable via the redox state of the polymer. Importantly, polymer alignment could blueshift the plasma wavelength and resonances by several hundreds of nanometers, forming a novel approach toward reaching the ultimate goal of redox‐tunable conducting polymer nanoantennas for visible light.
Traditional anisotropic nanoantennas have asymmetric shape. In this work, symmetry is instead broken by straining of a conducting polymer, leading to an in‐plane anisotropic plasma frequency. This enables circularly symmetric nanoantennas with polarization‐dependent localized surface plasmon resonances. The polarization dependence is consistent with inverse changes of the effective mass and mobility of thecharge carriers along different in‐plane directions.
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