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The material used for the dielectric layer in organic field-effect transistors strongly affects the efficiencies of the resulting devices. The reasons behind this connection, and opportunities to tune the device performance by changing the dielectric material, are now revealed.

Organic solar cells based on non-fullerene acceptors have enabled high efficiencies yet their charge dynamics and its impact on the photovoltaic parameters are not fully understood. Now, Chen et al. provide a general description of non-radiative voltage losses in both fullerene and non-fullerene solar cells.

High-performance organic solar cells call for novel designs of acceptor molecules. Here, He et al. design and synthesize a non-fullerene acceptor with an asymmetric structure for diverse donor:acceptor interfacial conformations and report a certificated power conversion efficiency of 18.2%.

Chemical doping allows for boosting the conductivity in conjugated polymers but the relationship between doping and the polymers’ complex, multiscale morphology remains elusive. Here the authors report that supramolecular chirality, which up to now had not been considered a parameter relevant to doping, significantly boosts the underpinning redox reaction in conjugated polymer thin films.

The solvent choice for processing organic solar cells impacts layer morphology and ultimately device performance. By controlling the molecular interactions, Zhang et al. realize a solvent-independent morphology that leads to high device efficiency.

Key optoelectronic properties for donor and acceptor organic semiconductors are identified to obtain organic solar cells with reduced open-circuit voltage losses and high power conversion efficiencies.

Fullerene acceptors are relevant for upscaling industrial production of organic solar cells. Here, authors reveal that for donor-acceptor blends with low energetic offset, charge transfer state dissociation rather than charge transfer state formation presents a bottleneck for free charge generation.

The performance of Y6-containing donor-acceptor active layers in organic solar cells is highly related to the charge-transfer nature in Y6 aggregates. Here, authors study charge-transfer characteristics of excitations of isolated and aggregated Y6 molecules through electroabsorption spectroscopy.

Previous descriptions of the charge-transfer absorptions in organic solar cells only involve the charge transfer state and the ground state. Here Chen et al. underline that a third state, i.e., the local absorbing state on the donor and/or acceptor, needs to be considered.

The electronic properties of organic molecules are sensitive to structural dynamics, but device control through this phenomenon has not been attained. Bakulinet al. show that the photoconductivity can be modulated by selective excitation of molecular vibrations in an organic optoelectronic device.

Organic radical molecules violating the Aufbau principle are shown to reach high luminescence quantum yield and photostability, with potential applications for deep-red and near-infrared light-emitting sources.

Y6, as a non-fullerene acceptor for organic solar cells, has attracted intensive attention because of the low voltage loss and high charge generation efficiency. Here, Zhang et al. find that the delocalization of exciton and electron wavefunction due to strong π-π packing of Y6 is the key for the high performance.

Molecular orientation profoundly affects the performance of donor-acceptor heterojunctions, whilst it has remained challenging to investigate the detail. Using a controllable interface, Ran et al. show that the edge-on geometries improve charge generation at the cost of non-radiative recombination loss.

Non-fullerene acceptors open the way to sensitive organic photodetectors for detecting circularly polarized near-infrared light.

The charge-transfer electronic states that form at the interfaces between electron-donor and electron-acceptor components have a key role in the electronic processes in organic solar cells. This Review describes the current understanding of how these charge-transfer states affect device performance.