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Understanding the charge-separation mechanism in organic photovoltaic cells (OPVs) could facilitate optimization of their overall efficiency. Here we report the time dependence of the separation of photogenerated electron hole pairs across the donor-acceptor heterojunction in OPV model systems. By tracking the modulation of the optical absorption due to the electric field generated between the charges, we measure ∼200 millielectron volts of electrostatic energy arising from electron-hole separation within 40 femtoseconds of excitation, corresponding to a charge separation distance of at least 4 nanometers. At this separation, the residual Coulomb attraction between charges is at or below thermal energies, so that electron and hole separate freely. This early time behavior is consistent with charge separation through access to delocalized π-electron states in ordered regions of the fullerene acceptor material.

Entanglement of states is one of the most surprising and counter-intuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which mediates the spin-conserving fission of one spin-0 singlet exciton into two spin-1 triplet excitons. Despite long theoretical and experimental exploration, the nature of the triplet-pair state and inter-triplet interactions have proved elusive. Here we use a range of organic semiconductors that undergo singlet exciton fission to reveal the photophysical properties of entangled triplet-pair states. We find that the triplet pair is bound with respect to free triplets with an energy that is largely material independent (∼30 meV). During its lifetime, the component triplets behave cooperatively as a singlet and emit light through a Herzberg–Teller-type mechanism, resulting in vibronically structured photoluminescence. In photovoltaic blends, charge transfer can occur from the bound triplet pairs with >100% photon-to-charge conversion efficiency. Singlet fission in organic semiconductors can generate triplet exciton pairs that are crucial to the charge generation in a photovoltaic process, whilst their nature remains elusive. Here, Yong et al . show that the immediate triplet pair is bound and emissive in a range of acene and heteroacene materials.

Singlet fission (SF) describes the conversion of a single photon-generated excited state into two triplet excitons through an initial singlet state. Despite its significance for solar energy applications, the relationship between microstructure, temperature, and SF efficiency remains poorly understood. Using cryogenic fluorescence microscopy, we correlate primary singlet fission (PSF) efficiency with local film morphology in a prototypical high-efficiency anthradithiophene (diF-TES-ADT) thin film. Our hyperspectral microscopy measurements of absorption and emission with sub-micron resolution reveal spatially inhomogeneous PSF efficiency that correlates directly with local crystallinity. Temperature- and time-resolved spectroscopy demonstrate that enhanced PSF efficiency in highly crystalline regions results from favorable endothermic alignment of a charge-transfer (CT) state. These findings emphasize how spatial inhomogeneity critically impacts SF film performance and caution against relying solely on spatially averaged metrics when evaluating SF materials.

Singlet fission and triplet–triplet annihilation represent two highly promising ways of increasing the efficiency of photovoltaic devices. Both processes are believed to be mediated by a biexcitonic triplet-pair state, 1(TT). Recently however, there has been debate over the role of 1(TT) in triplet–triplet annihilation. Here we use intensity-dependent, low-temperature photoluminescence measurements, combined with kinetic modelling, to show that distinct 1(TT) emission arises directly from triplet–triplet annihilation in high-quality pentacene single crystals and anthradithiophene (diF-TES-ADT) thin films. This work demonstrates that a real, emissive triplet-pair state acts as an intermediate in both singlet fission and triplet–triplet annihilation and that this is true for both endo- and exothermic singlet fission materials.The role of the biexcitonic triplet-pair state 1(TT) during triplet–triplet annihilation events in singlet-fission materials has been the subject of recent debate. Now, emissive 1(TT) states have been shown to be direct products of triplet–triplet annihilation in both endothermic and exothermic singlet-fission materials.

Under intense laser excitation, thin films and suspensions of graphite and its nanostructure, including carbon black, nanotubes, few-layer graphenes and graphene oxides, exhibit induced transparency due to saturable absorption. This switches to optical limiting only at very high fluences when induced breakdown gives rise to microbubbles and microplasmas that causes nonlinear scattering. Here, we show that dispersed graphenes, in contrast, can exhibit broadband nonlinear optical absorption at fluences well below this damage threshold with a strong matrix effect. We obtained, for nanosecond visible and near-infrared pulses, a new benchmark for optical energy-limiting onset of 10 mJ cm −2 for a linear transmittance of 70%, with excellent output clamping in both heavy-atom solvents and polymer film matrices. Nanosecond pump–probe spectroscopy in chlorobenzene reveals that the nanographene domains switch from the usual broadband photo-induced bleaching to a novel reverse saturable absorption mechanism with increasing excitation densities across this threshold. Researchers show that dispersed functionalized graphene can exhibit broadband nonlinear optical absorption at fluences well below the damage threshold. An optical energy-limiting onset benchmark of 10 mJ cm −2 at a linear transmittance of 70% was obtained for nanosecond visible and near-infrared pulses. The findings shed light on the formation of practical thin films with broadband optical limiting characteristics.

High-spin states in molecular systems hold significant interest for applications ranging from optoelectronics to quantum technologies. Spin states generated in intramolecular singlet fission are of particular relevance, yet the mechanisms controlling triplet-pair formation are not fully understood – especially the involvement of quintet states in luminescence at room temperature remains experimentally elusive. Here, we investigate high-spin state formation and emission in dimers and trimers comprising multiple diphenylhexatriene units. We demonstrate the formation of pure quintet states in all these oligomers, with quintet-mediated emission dominating delayed fluorescence up to room temperature. By distinguishing between the formation of weakly exchange-coupled triplet pairs and triplet excitons generated by intersystem crossing, we identify the methylated trimer as the only oligomer exhibiting exclusively the desired singlet fission route. These findings establish quintet-mediated delayed emission as a distinct spin-selective pathway and show how molecular structure directs high-spin formation, opening opportunities for room-temperature molecular quantum technologies. This study reveals high-spin state formation and quintet-mediated emission in diphenylhexatriene oligomers. Quintet states dominate delayed fluorescence up to room temperature, establishing a spin-selective platform for quantum technologies.

Photons as information carriers have the potential to meet the ever-increasing demands on bandwidth and information density in fields such as information and communication technology, biomedicine and computing. Organic semiconductors may be well-suited to such applications, thanks to their ability to transmit, modulate and detect light in an architecture that is low cost, flexible, lightweight and robust. Here we review recent breakthroughs in organic photonics, including ultrafast all-optical modulation in polymer photonic crystals, silicon/organic hybrid systems, gain switching in polymer amplifiers and lasers, and new devices such as hybrid organic/inorganic electrically pumped lasers. The increasing capability for manufacturing a wide variety of optoelectronic devices from polymer and polymer–silicon hybrids, including transmission fibre, modulators, detectors and light sources, suggests that organic photonics has a promising future in communications and other applications.

Polaritons are quasi-particles composed of a superposition of excitons and photons that can be created within a strongly coupled optical microcavity. Here, we describe a structure in which a strongly coupled microcavity containing an organic semiconductor is coupled to a second microcavity containing a series of weakly coupled inorganic quantum wells. We show that optical hybridisation occurs between the optical modes of the two cavities, creating a delocalised polaritonic state. By electrically injecting electron–hole pairs into the inorganic quantum-well system, we are able to transfer energy between the cavities and populate organic-exciton polaritons. Our approach represents a new strategy to create highly efficient devices for emerging ‘polaritonic’ technologies.

Optimizing the orientation, crystallinity, and domain size of components within organic photovoltaic (OPV) devices is key to maximizing their performance. Here a broadly applicable approach for enhancing the morphology of bulk heterojunction OPV devices using metal–organic nanosheets (MONs) as additives is demonstrated. It is shown that addition of porphyrin‐based MONs to devices with fully amorphous donor polymers lead to small improvements in performance attributed to increased light absorption due to nanosheets. However, devices based on semi‐crystalline polymers show remarkable improvements in power conversion efficiency (PCE), more than doubling in some cases compared to reference devices without nanosheets. In particular, this approach led to the development of PffBT4T2OD‐MON‐PCBM device with a PCE of 12.3%, which to the authors’ knowledge is the highest performing fullerene based OPV device reported in literature to date. Detailed analysis of these devices shows that the presence of the nanosheets results in a higher fraction of face‐on oriented polymer crystals in the films. These results therefore demonstrate the potential of this highly tunable class of two‐dimensional nanomaterials as additives for enhancing the morphology, and therefore performance, of semi‐crystalline organic electronic devices. Porphyrin based metal‐organic framework nanosheets are added to a range of organic photovoltaic devices resulting in the highest performing fullerene based devices reported to date. Analysis shows that for devices based on semi‐crystalline polymers, the nanosheets increase the fraction of face‐on oriented polymer crystals in the films leading to enhanced absorbance and charge transport.

Schiff and Burgart examine the ethical, legal, and social justice concerns surrounding mandatory or routine pregnancy testing (PT) in US emergency departments (EDs). They state that such tests are often conducted without patient consent, which undermines autonomy and other key ethical principles. Following the 2022 Dobbs decision that removed federal abortion protections, learning one's pregnancy status can have serious legal and personal consequences depending on the state. They argue that routine PT in the ED is legally problematic, dismissive of patients' own reports about their pregnancy status and sexual history, and conflicts with LGBTQIA+ rights. Additionally, the widespread use of PTs without clear clinical justification is economically inefficient. They advocate for healthcare ethics consultations to help ensure ED practices respect patient rights and align with ethical, legal, and social justice standards in today's complex socio-political environment.