Transport in organic and hybrid semiconductors

Organic and hybrid semiconductors combine electronic functionality, synthetic tunability, and mechanical flexibility, enabling a broad spectrum of technologies, from transistors and light emitting diodes (LEDs) to solar cells, sensors, and neuromorphic systems. Their chemical versatility allows for fine control over energy levels, morphologies, and processability, supporting scalable, low-cost fabrication on flexible substrates. Over the past three decades, the field has evolved from fundamental materials discovery to application-oriented research, leading to notable commercial successes and growing industrial interest. Yet, a central challenge persists: understanding and controlling charge transport in these intrinsically disordered and heterogeneous systems. Unlike crystalline inorganic semiconductors, charge transport in organic and hybrid materials is highly sensitive to local morphology, energetic disorder, interfacial effects, and dynamic interactions with the environment. Addressing these complexities is essential not only for improving device performance but also for unlocking new functionalities.

This themed collection brings together recent advances that deepen our understanding of charge transport in organic and hybrid systems and showcases new materials, characterization techniques, and device concepts aimed at pushing the performance and reliability of next-generation technologies.

Several contributions highlight the critical role of molecular design in dictating charge transport across diverse material classes and device platforms. For instance, Huang et al. [https://doi.org/10.1039/D5TC00295H] demonstrate how a simple end-capping strategy using strong electron-withdrawing groups can enhance π–π stacking interactions, which leads to improved mobilities in ambipolar and n-type channel polymer field-effect transistors (FETs). Che et al. [https://doi.org/10.1039/D5TC01650A] design azo-benzodifurandione-based polymers that combine high mobility with mechanical resilience under up to 50% strain, enabling stretchable n-type FETs. Focusing on ionic side chains, Chouhan et al. [https://doi.org/10.1039/D5TC01491C] compare anionic and cationic conjugated polyelectrolytes for pseudocapacitors, revealing how pendant group polarity impacts doping, ion transport, and capacitance. Nishimoto et al. [https://doi.org/10.1039/D5TC01735A] design quinoidal propylenedioxythiophene dimers as a new approach for air-stable n-type semiconductors, showing that modifying side chains can influence both solubility and crystallinity for improved charge transport. Extending to hybrid semiconductors, Jansen et al. [https://doi.org/10.1039/D5TC01143D] explore compositional tuning in Cs-based perovskites, showing that small additions of formamidinium and optimized solvent processing enhance film morphology and charge transport, ultimately boosting the performance of green light-emitting diodes.

Beyond molecular design, doping strategies, processing methods, and interfacial engineering are also shown to shape morphology and charge transport dynamics. Kawasaki et al. [https://doi.org/10.1039/D5TC01263E] present a cation replacement approach using bicyclic guanidinium salts to achieve thermally stable n-type doping in carbon nanotubes, resulting in improved conductivity and thermoelectric performance. Kuklinski et al. [https://doi.org/10.1039/D5TC00502G] introduce a two-step spin-coating method to grow phase-pure thin films of Cs₂TeBr₆, a vacancy-ordered double perovskite, and demonstrate hopping-based hole transport in single-carrier diodes. Wang et al. [https://doi.org/10.1039/D5TC01169H] develop a sol–gel approach to fabricate CuBO₂ hole transport layers, enabling efficient and stable p–i–n perovskite solar cells with power conversion efficiencies exceeding 18%. On the organic side, Rodríguez-Martínez et al. [https://doi.org/10.1039/D5TC01473E] show that co-solvent selection modulates the structural ordering of donor and acceptor domains in PBDB-T:ITIC blends, influencing both photovoltaic performance and long-term shelf stability. Ghobadi et al. [https://doi.org/10.1039/D5TC01378J] also explore interfacial engineering, showing that incorporating an ultrathin Al₂O₃ layer at the semiconductor–dielectric interface can significantly improve carrier mobility and subthreshold swing in polymer ferroelectric transistors. Lastly, Irimia-Vladu et al. [https://doi.org/10.1039/D5TC01419K] highlight the potential of using natural waxes as low-cost, low-voltage dielectrics for organic field-effect transistors (OFETs).

In parallel, several contributions deepen our understanding of transport mechanisms through advanced modeling and simulation approaches. Dörfler et al. [https://doi.org/10.1039/D5TC01487E] revisit the widely used Miller–Abrahams rate in kinetic Monte Carlo simulations, demonstrating that this commonly used approximation can misrepresent mobility trends under low disorder or high electric field conditions. Cristofaro et al. [https://doi.org/10.1039/D5TC01620G] employ molecular dynamics simulations to reveal how nanoscale morphological heterogeneity in semiconducting polymers leads to significant variations in mechanical properties, which are intimately linked to local charge transport behavior. Moving to inorganics, Claes et al. [https://doi.org/10.1039/D5TC01708D] use first-principles calculations to investigate transport in Sn(II) oxides; they identify ternary compositions with hole mobilities comparable to state-of-the-art transparent conductive oxides and clarify how specific vibrational modes influence electron–phonon scattering.

Emerging applications showcase how transport phenomena enable novel device functionalities. Hayakawa et al. [https://doi.org/10.1039/D5TC01712B] exploit controlled hole- and electron-trapping in a floating-gate organic antiambipolar transistor to enable reconfigurable synaptic behavior. Wang et al. [https://doi.org/10.1039/D4TC04363D], develop a bipolar synaptic transistor where an electret layer and charge trapping allow dynamic switching between excitatory and inhibitory modes.

Together, these contributions reflect the diversity of strategies being developed to tackle the transport challenges inherent to soft organic and hybrid semiconductors. We hope that this collection not only provides an overview of recent progress but also stimulates further cross-disciplinary research in the field. As organic and hybrid electronics continue to evolve, understanding and exploiting charge transport will be key to unlocking new device functionalities and performance benchmarks.

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