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Homojunction intermolecular charge separation is reported in photoexcited anion–cation pairs induced by external electric field bias, opening possibilities for light harvesting using molecular semiconductors.

Thermoelectric materials are required to be electrically conducting while thermally insulating, which can be challenging to achieve. Here, the authors report a thermoelectric transport regime with defect tolerant charge transport but defect intolerant heat propagation in two-dimensional coordination polymer films.

Controlling electron spin states with light is vital for quantum technologies but requires electronic excitations with net spin. Now a molecular diradical with two trityl radical groups coupled via a meta-linked fluorene bridge has been developed that features luminescent singlet and triplet excitons. The spins in the ground state can be written and read using photons, giving rise to broad magnetic and microwave modulation of the photoluminescence.

Chemical functionalization of graphene is a useful method for modulating its properties, although this is limited by a lack of control and resulting in poorly defined structures. Here the authors report the atomically precise chlorination of nanographenes and apply the methods to graphene nanoribbons.

Thermally activated delayed fluorescence is a mechanism for enhancing the efficiency of organic light emitting diodes by harvesting triplet excitons, but there is still a need to design more efficient materials. Here, the authors rationally design and characterize a series of π-extended boron- and nitrogen-doped nanographenes as promising candidates.

Singlet exciton fission produces two triplet excited states from one excited singlet through interchromophoric coupling, which is thought to require local order. Now, a triplet yield of 200% and diffusion-limited triplet formation are reported in solutions of TIPS pentacene. Kinetic studies revealed an excimer intermediate and enabled suggestions of design principles for the promotion of singlet fission.

Understanding how excited states behave at heterojunctions between polymers in blends is fundamental to designing better organic solar cells and light-emitting diodes. A quantum-mechanical molecular-scale model of how excitations behave at heterojunctions has been developed, showing an unexpectedly wide but specific range of excitonic states.

Singlet fission — the splitting of a singlet exciton into two triplets — is a process that could be exploited to improve the power conversion efficiency of solar cells. Spectroscopic data now suggest that coherent and incoherent mechanisms for singlet fission in crystalline hexacene coexist and occur on different timescales.

A low singlet-triplet energy gap, necessary for delayed fluorescence organic semiconductors, results in a small radiative rate that limits performance in OLEDs. Here, the authors show that it is possible to reconcile these conflicting requirements in materials that can access both high oscillator strength intramolecular excitations and intermolecular charge transfer states.

MXenes with borate polyanion terminations are synthesized using a flux-assisted eutectic molten etching approach. These triatomic-layer terminations empower MXenes with considerably improved charge transport and charge storage capabilities.

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.

Dynamic disorder reduces the carrier mobility in organic semiconductors (OSs) to an extent that depends on their specific electronic band structure. Here the authors study the temperature-dependent hole mobility of two structurally similar OSs and find that thermal access to transiently delocalized states enhances hole mobility in C8-DNTT-C8 compared to DNTT.

The role of the dielectric environment in thermally activated delayed fluorescence (TADF) is not yet fully understood. Here the authors reveal the relevance of environment–emitter interactions in gating the reverse intersystem crossing and its particular relevance in dipolar TADF emitters.

Exploiting the energy transfer between the host triplet states and spin doublet exciton states of a radical organic emitter enables near-infrared organic light-emitting diodes with an external quantum efficiency up to 9.6% at an emission wavelength of 800 nm.

Measurements and simulations of several high-mobility conjugated polymers show that their charge transport properties reflect an almost complete lack of disorder in the polymers, despite their amorphous microstructures, resulting from the resilience of the planar polymer backbone conformations to side-chain disorder.

We report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with high spin multiplicity, simultaneously supporting a high efficiency of initialization, spin manipulations and light-based readout at room temperature.

Mixed ionic–electronic transport in conducting polymers remains poorly understood. Here the authors observe non-equilibrium electronic transport when counterions are unable to equilibrate in response to gate-injected electronic carriers.

Artificial light-harvesting systems cannot self-assemble into photon-capturing structures that can reversibly switch into an inactive state. Here, the authors describe a simple and robust dipeptide construct which self-assembles to fibrils, platelets or nanospheres with varying optical properties.

A simple manipulation of an electrolyte’s glass transition enables nanoresolved electrochemical ion implantation doping in a variety of polymeric semiconductors.

Spin and charge dynamics are inevitably linked, the study of the one often illuminating the other. Here, the authors study spin relaxation in ambipolar polymers and, backed by simulations, show how charge dynamics and wavefunction localization together set relaxation times up to room temperature.

High-resolution resonant impulsive stimulated Raman spectroscopy in two-dimensional hybrid metal halide perovskites provides evidence for polaronic effects on excitons, which couple to distinct low-frequency vibrational modes of the ionic lattice.

Though single-material organic solar cells are attractive for next-generation photovoltaic technologies, designing new materials with ideal properties remains a challenge. Here, the authors report the use of orientation-dependent molecular electrostatics to realise efficient homojunction devices.

Optically dark (non-emitting) triplet excitons on organic molecules may be rendered bright by coupling the molecules to lanthanide-doped nanoparticles, providing a way to control such excitons in optoelectronic systems.

Designing conjugated polymers with high charge carrier mobility and fluorescence quantum efficiency, though attractive for optoelectronics, remains challenging. Here, the authors report a strategy for designing donor-acceptor copolymers whose optoelectronic properties exceed the state-of-the-art.

Linear π-conjugated polymers have attracted great attention as semiconductors for (opto)electronic devices, but charge transfer is only effective along polymer chains. Here poly(benzimidazobenzophenanthroline)-ladder-type two-dimensional conjugated polymers are presented with high charge carrier mobilities.

The use and characterization of graphene quantum dots is limited by their pronounced tendency to form aggregates. Here, the authors synthesize rod-shaped motifs of nanographenes with up to 132 sp² carbon atoms that are fully individualized, which allows the precise description of their intrinsic photophysical properties.

Two-dimensional material heterostructures enable unique electronic features by introducing periodic potentials. Here, Gobbiet al. use a monolayer supramolecular lattice with a tunable one-dimensional periodic potential to modify the electronic structure of graphene.

Interesting changes in physical and optical properties can result from the binding of small molecules to supramolecular polymers. Here, the authors present an ATP assay, using a supramolecular helix to switch between left- and right-handed conformations on binding different adenosine phosphates.

The electronic and optical properties of polymer semiconductors are largely dictated by their chemical structure. This study examines the nature of the photoexcited states generated in donor–acceptor polymers, and uncovers the dynamics of polaron pairs generation and recombination.

The charge transport mechanism in MXenes—an emerging class of layered materials—is not yet fully understood. A combination of terahertz spectroscopy and transport measurements shows that the formation of large polarons play a crucial role.

The long spin lifetimes observed in polymeric semiconductors hold promise for potential applications. A careful study untangles the main mechanism behind them.

Photochromic molecules offer the unique opportunity to demonstrate multifunctional devices with light-tunable electrical characteristics. Gobbi et al. build light-switchable electronic heterojunctions based on atomically precise, photo-reversible molecular superlattices on graphene and MoS₂.

To unlock the potential of biological semiconductors for printed flexible electronics, experimental evidence that reveals the material’s charge transport mechanism is required. Here, the authors report the charge transport mechanism in hydrogen-bonded DNA topoisomerase inhibitors.

The microstructure of organic semiconductors affects their transport properties, but directly probing this relationship is challenging. He et al. show that step edges act as electron traps on the surfaces of n-type single crystals, resulting in a field effect transistor mobility that depends on step density.

Photochemical isomerisation can engender large conformational rearrangements, giving rise to switchable physical and electronic properties. Here, the authors use azo-benzene derivatives as addressable surfactants to facilitate the exfoliation of graphene and provide light activated modulation.

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, Yonget al. show that the immediate triplet pair is bound and emissive in a range of acene and heteroacene materials.

Martensitic transition is commonly seen in steel and shape memory alloys but rarely in organic materials. Chung et al. discover martensitic transitions in organic electronics and utilize it in designing field-effect transistors, leading to shape memory effect that in return modifies charge transport properties.

Localized photodoping in mixed-cation perovskites is shown to modify charge-carrier recombination and thus offer a route for more efficient light emission.

Exciton-polaritons are typically formed in organic systems when the molecules are confined between metallic or dielectric mirrors. Here, the authors reveal that interactions between excitons and moderately confined photonic states within the bare organic film can also lead to polariton formation, making them the primary photoexcitation.