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A new yellow-emitting quadrupolar donor–π–acceptor–π–donor (D–π–A–π–D) molecule compound has been synthesised featuring benzo-[1,2-c:4,5-c′]dithiophene-4,8-dione as the acceptor. This molecule was prepared for the purpose of elucidating the origins of the very low photoluminescence quantum yield encountered in its thermally activated delayed fluorescent (TADF) red-emitting isomer which used benzo-[1,2-b:4,5-b′]dithiophene-4,8-dione as the acceptor. The molecule was designed to circumvent the energy gap law, by having a wider HOMO–LUMO gap, while retaining a comparable singlet–triplet gap but ultimately demonstrates even weaker photoluminescence than the red isomer. It shows extremely fast intersystem crossing followed by rapid non-radiative decay and no observable TADF. The electronic structure of this new molecule has been studied using cyclic voltammatery alongside steady-state and transient optical spectroscopy, with observations underpinned by computational insights. To identify whether the observations made from the experimental results might be general properties of benzodithiophene-4,8-dione containing emitters, a computational study is extended to the four isomers of benzodithiophene-4,8-dione in comparison with 9,10-anthraquinone. The results suggest that the singlet and triplet manifolds of these systems are strongly coupled via spin–orbit interactions, and explain how the relative electron-accepting strength of these quinones arises from an interplay between the resonance gains or losses of the central benzene and fused thiophene rings upon photoexcitation. This provides valuable insights into the design principles required for efficient organic light-emitting materials. [ABSTRACT FROM AUTHOR]

The use of non-fullerene acceptors (NFAs) in organic solar cells has led to power conversion efficiencies as high as 18%.sup.1. However, organic solar cells are still less efficient than inorganic solar cells, which typically have power conversion efficiencies of more than 20%.sup.2. A key reason for this difference is that organic solar cells have low open-circuit voltages relative to their optical bandgaps.sup.3, owing to non-radiative recombination.sup.4. For organic solar cells to compete with inorganic solar cells in terms of efficiency, non-radiative loss pathways must be identified and suppressed. Here we show that in most organic solar cells that use NFAs, the majority of charge recombination under open-circuit conditions proceeds via the formation of non-emissive NFA triplet excitons; in the benchmark PM6:Y6 blend.sup.5, this fraction reaches 90%, reducing the open-circuit voltage by 60 mV. We prevent recombination via this non-radiative channel by engineering substantial hybridization between the NFA triplet excitons and the spin-triplet charge-transfer excitons. Modelling suggests that the rate of back charge transfer from spin-triplet charge-transfer excitons to molecular triplet excitons may be reduced by an order of magnitude, enabling re-dissociation of the spin-triplet charge-transfer exciton. We demonstrate NFA systems in which the formation of triplet excitons is suppressed. This work thus provides a design pathway for organic solar cells with power conversion efficiencies of 20% or more. A substantial pathway for energy loss in organic solar cells may be suppressed by engineering hybridization between non-fullerene acceptor triplet excitons and spin-triplet charge transfer excitons., Author(s): Alexander J. Gillett [sup.1] , Alberto Privitera [sup.2] , Rishat Dilmurat [sup.3] , Akchheta Karki [sup.4] , Deping Qian [sup.5] , Anton Pershin [sup.3] [sup.6] , Giacomo Londi [sup.3] [...]

Carbene‐metal‐amides (CMAs) are emerging delayed fluorescence materials for organic light‐emitting diode (OLED) applications. CMAs possess fast, efficient emission owing to rapid forward and reverse intersystem crossing (ISC) rates. The resulting dynamic equilibrium between singlet and triplet spin manifolds distinguishes CMAs from most purely organic thermally activated delayed fluorescence emitters. However, direct experimental triplet characterization in CMAs is underutilized, limiting our detailed understanding of the ISC mechanism. In this work, we combine time‐resolved spectroscopy with tuning of state energies through environmental polarity and metal substitution, focusing on the interplay between charge‐transfer (3CT) and local exciton (3LE) triplets. Unlike previous photophysical work, we investigate evaporated host : guest films of CMAs and small‐molecule hosts for increased device relevance. Transient absorption reveals an evolution in the triplet excited‐state absorption (ESA) consistent with a change in orbital character between hosts with differing dielectric constants. Using quantum chemical calculations, we simulate ESAs of the lowest triplet states, highlighting the contribution of only 3CT and donor‐moiety 3LE states to spectral features, with no strong evidence for a low‐lying acceptor‐centered 3LE. Thus, our work provides a blueprint for understanding the role of triplet excited states in CMAs which will enable further intelligent optimization of this promising class of materials. [ABSTRACT FROM AUTHOR]

Kemmerer's discussion of links between semantic typology and embodied cognition is welcome, especially his survey of available evidence. Focusing on mechanisms of embodied enculturation, however, we must understand that language is just one part of developmental assemblies that shape cognition, alongside other cultural elements such as sensory learning, behavior patterns, social interactions, and emotional experience. We believe that a source of this problem is an obsolete definition of "culture" as shared mental information that is inconsistent with models of embodied cognition and yet pervasive in human and cognitive sciences. We point to microethnographies of cognitive ecologies as a tractable remedy. Embodied cognition is encultured by mechanisms in addition to language, including sensory learning, behavior, interaction, and emotion. An obsolete definition of culture as "shared information" can obscure this developmental assembly that microethnography explores. [ABSTRACT FROM AUTHOR]

Non‐fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open‐circuit voltage of OSCs remains low relative to their optical gap due to excessive non‐radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non‐geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet‐triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out‐of‐plane ordering. Since TTA converts a fraction of the non‐emissive triplet states into bright singlet states, it has the potential to reduce non‐radiative voltage losses. Through a kinetic analysis of the recombination processes under 1‐Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non‐radiative voltage losses by up to several tens of millivolts. [ABSTRACT FROM AUTHOR]

The great progress in organic photovoltaics (OPV) over the past few years has been largely achieved by the development of non-fullerene acceptors (NFAs), with power conversion efficiencies now approaching 20%. To further improve device performance, loss mechanisms must be identified and minimized. Triplet states are known to adversely affect device performance, since they can form energetically trapped excitons on low-lying states that are responsible for non-radiative losses or even device degradation. Halogenation of OPV materials has long been employed to tailor energy levels and to enhance open circuit voltage. Yet, the influence on recombination to triplet excitons has been largely unexplored. Using the complementary spin-sensitive methods of photoluminescence detected magnetic resonance and transient electron paramagnetic resonance corroborated by transient absorption and quantum-chemical calculations, exciton pathways in OPV blends are unravelled employing the polymer donors PBDB-T, PM6, and PM7 together with NFAs Y6 and Y7. All blends reveal triplet excitons on the NFA populated via non-geminate hole back transfer and, in blends with halogenated donors, also by spin-orbit coupling driven intersystem crossing. Identifying these triplet formation pathways in all tested solar cell absorber films highlights the untapped potential for improved charge generation to further increase plateauing OPV efficiencies. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) have recently shown a rapid improvement in their performance, bringing power conversion efficiencies to above 18%. However, the open‐circuit voltage of OSCs remains low relative to their optical gap and this currently limits efficiency. Recombination to spin‐triplet excitons is a key contributing factor, and is widely, but not universally, observed in donor–acceptor blends using both fullerene and nonfullerenes as electron acceptors. Here, an experimental framework that combines time‐resolved optical and magnetic resonance spectroscopies to detect triplet excitons and identify their formation mechanisms, is reported. The methodology is applied to two well‐studied polymer:fullerene systems, PM6:PC60BM and PTB7‐Th:PC60BM. In contrast to the more efficient nonfullerene acceptor systems that show only triplet states formed via nongeminate recombination, the fullerene systems also show significant triplet formation via geminate processes. This requires that geminate electron–hole pairs be trapped long enough to allow intersystem crossing. It is proposed that this is a general feature of fullerene acceptor systems, where isolated fullerenes are known to intercalate within the alkyl sidechains of the donor polymers. Thus, the study demonstrates that engineering good donor and acceptor domain purity is key for suppressing losses via triplet excitons in OSCs. [ABSTRACT FROM AUTHOR]

Efficient organic emitters in the deep‐red region are rare due to the "energy gap law". Herein, multiple boron (B)‐ and nitrogen (N)‐atoms embedded polycyclic heteroaromatics featuring hybridized π‐bonding/ non‐bonding molecular orbitals are constructed, providing a way to overcome the above luminescent boundary. The introduction of B‐phenyl‐B and N‐phenyl‐N structures enhances the electronic coupling of those para‐positioned atoms, forming restricted π‐bonds on the phenyl‐core for delocalized excited states and thus a narrow energy gap. The mutually ortho‐positioned B‐ and N‐atoms also induce a multi‐resonance effect on the peripheral skeleton for the non‐bonding orbitals, creating shallow potential energy surfaces to eliminate the high‐frequency vibrational quenching. The corresponding deep‐red emitters with peaks at 662 and 692 nm exhibit narrow full‐width at half‐maximums of 38 nm, high radiative decay rates of ca. 108 s−1, ≈100 % photo‐luminescence quantum yields and record‐high maximum external quantum efficiencies of ca. 28 % in a normal planar organic light‐emitting diode structure, simultaneously. [ABSTRACT FROM AUTHOR]

The power conversion efficiencies (PCEs) of single‐junction organic solar cells (OSC) have now reached over 18%. This rapid recent progress can be attributed to the development of new nonfullerene electron acceptors (NFAs) that are paired with suitable high performing polymer electron donors. Substantial improvements in the PCEs and long‐term stability enabled by NFA OSCs have allowed the development and integration of these systems into many niche and novel applications. Here, the recent progress that has been made in understanding the device photophysics of high performing polymer:NFA blends is highlighted. As the bulk heterojunction morphology is intrinsically linked to the device photophysics, this review focuses on studies that have provided noteworthy morphological insights using advanced techniques such as solid‐state NMR and resonant soft X‐ray scattering. Through this, some of the major challenges that must be overcome to attain PCEs of over 20% in NFA OSCs are addressed. [ABSTRACT FROM AUTHOR]

Even though significant breakthroughs with over 18% power conversion efficiencies (PCEs) in polymer:non‐fullerene acceptor (NFA) bulk heterojunction organic solar cells (OSCs) have been achieved, not many studies have focused on acquiring a comprehensive understanding of the underlying mechanisms governing these systems. This is because it can be challenging to delineate device photophysics in polymer:NFA blends comprehensively, and even more complicated to trace the origins of the differences in device photophysics to the subtle differences in energetics and morphology. Here, a systematic study of a series of polymer:NFA blends is conducted to unify and correlate the cumulative effects of i) voltage losses, ii) charge generation efficiencies, iii) non‐geminate recombination and extraction dynamics, and iv) nuanced morphological differences with device performances. Most importantly, a deconvolution of the major loss processes in polymer:NFA blends and their connections to the complex BHJ morphology and energetics are established. An extension to advanced morphological techniques, such as solid‐state NMR (for atomic level insights on the local ordering and donor:acceptor ππ interactions) and resonant soft X‐ray scattering (for donor and acceptor interfacial area and domain spacings), provide detailed insights on how efficient charge generation, transport, and extraction processes can outweigh increased voltage losses to yield high PCEs. [ABSTRACT FROM AUTHOR]

Employing the thiophene based quinone, benzo[1,2-b:4,5-b′]dithiophene-4,8-dione, as the electron-accepting moiety alongside N-phenylcarbazole donors to produce a donor–π–acceptor–π–donor (D–π–A–π–D) molecule has yielded a new red emitter displaying delayed fluorescence. This new molecule shows strongly (over 100 nm) red-shifted emission when compared to an anthraquinone based analogue. Cyclic voltammetry complemented by computational insights prove that this red-shift is due to the significantly stronger electron-accepting ability of the thiophene quinone compared to anthraquinone. Photophysical and computational studies of this molecule have revealed that while the presence of the thiophene containing acceptor facilitates rapid intersystem crossing which is comparable to anthraquinone analogues, the reverse intersystem crossing rate is slow and non-radiative decay is rapid which we can attribute to low-lying locally excited states. This limits the total photoluminescence quantum efficiency to less than 10% in both solution and the solid state. These results provide a useful example of how very minor structural variations can have a defining impact on the photophysical properties of new molecular materials. [ABSTRACT FROM AUTHOR]

We agree with Bruineberg and colleagues' main claims. However, we urge for a more forceful critique by focusing on the extended mind debate. We argue that even once the Pearl and Friston versions of the Markov blanket have been untangled, that neither is sufficient for tackling and resolving the question of demarcating the boundaries of the mind. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials are expected to address triplet‐related losses in electrically driven organic lasers, as the electrically generated triplets in the materials can be converted to radiative singlets through reverse intersystem crossing (RISC). This offers a way to bypass triplet absorption and annihilation in organic semiconductor lasers (OSLs). In this work, two versatile TADF emitters 4tCzPz and 4αCbPz for application in organic light‐emitting diodes (OLEDs) and OSLs are presented. Both emitters possess moderately high singlet‐triplet energy gap, ΔEST (≈0.30 eV) and show high photoluminescence quantum yields, ΦPL, in solution and solid‐state and prominent stimulated emission features in solution. Films of 4tCzPz and 4αCbPz doped in mCBP show an amplified spontaneous emission (ASE) threshold of 41.0 and 44.9 µJ/cm2, respectively. The OLEDs with 4tCzPz and 4αCbPz emit with peak wavelengths of 492 and 475 nm, respectively, and show corresponding maximum external quantum efficiencies, EQEmax, of 24.6 and 21.3%. The research shows that D‐A TADF materials hold significant potential not only as emitters for OLEDs but also in OSLs. [ABSTRACT FROM AUTHOR]