Doping in Organic Semiconductors: Fundamentals, Materials, and Applications

The controlled doping of organic semiconductors has emerged as a central research direction in organic electronics, driven by the recognition that precise manipulation of carrier density is essential for fully exploiting the unique properties of these materials. Symposium T at the 2024 Spring Meeting of the European Materials Research Society (E-MRS) underscored the need for a deeper and more unified understanding of these processes. The invited contributions assembled in this Special Issue of Advanced Electronic Materials reflect the significant progress being made toward predictive doping strategies and rational materials design. One major theme addressed in this collection is the advancement of n-type doping and its implications for organic thermoelectrics. Several articles demonstrate how molecular structure, regiochemistry, and processing conditions determine the efficiency and stability of n-doped systems. Fullerene derivatives with controlled regiochemistry (202500287) reveal how crystallinity and dopant miscibility influence both conductivity and thermoelectric performance. Benzodifuranone copolymers exhibit greatly enhanced electronic transport when high backbone alignment is combined with sequential doping using N-DMBI-H. (202500047). Structural variations in benzodifuranone–isatin acceptor polymers (202500213) further demonstrate how backbone conformation governs morphology and ultimately thermoelectric behavior. The study of charge injection and transport in isoindigo–bithiophene polymers (202500098) provides insights into how molecular structure governs doped transport in field-effect devices. The contributions (202400988, 202400767) further extend the range of n-type materials and doping strategies by introducing new molecular backbones, dopant–polymer combinations, and process-compatible approaches. Together, these studies advance the understanding and application of n-type doping in organic semiconductors. Progress in p-type doping and hybrid transport systems is also well represented. The use of proton-coupled electron transfer enables bandgap-dependent doping in semiconducting carbon nanotube networks (202400817), where the doping level depends on both the chemical environment and the nanotube diameter. Hybrid thermoelectric composites, formed by wrapping semiconducting carbon nanotubes with a p-type polymer (202400216), demonstrate how interfacial design can promote delocalized charge transport. Improvements in dip-coated conjugated polymer films (202400695) show that processing conditions, particularly the Landau–Levich and evaporation regimes, which govern polymer packing and dopant–host interactions, have a decisive influence on thermoelectric performance. Redox-active copolymer films based on vinyl(triphenylamine) and styrene (202500645) provide a model system to study mixed ionic–electronic conduction, where variations in crosslinking density and polymer architecture directly influence reversible redox behavior, ionic uptake, and charge compensation processes. A third group of contributions provides fundamental insight into the microscopic mechanisms that control dopant mobility, phase behavior, and spatial distribution. Thermal activation induces dopant diffusion and phase segregation in polymeric blends (202500170), strongly affecting both the electronic structure and the stability of the doped material. Computational microscopy of doped conjugated polymers (202400662) reveals largely random dopant distributions rather than significant clustering, offering a more realistic representation of the doped state and informing future models of transport. The articles collected in this Special Issue demonstrate substantial progress in understanding and controlling doping in organic semiconductors. Advances in n-type molecular design, the development of hybrid and composite transport systems, and increasingly detailed insights into dopant dynamics all point toward the possibility of achieving far greater control over doping processes. These developments are expected to enable not only more stable, efficient, and versatile organic electronic devices but also to facilitate new opportunities for applications in energy harvesting, flexible electronics, and bio-integrated technologies, where precisely tuned charge transport is essential. The author thank the financial support of the Ministry of Science, Innovation and Universities of Spain, under Grants ID2024-163109OA-I00 and CEX2019-000917-S in the framework of the Spanish Severo Ochoa Centre of Excellence. The authors declare no conflicts of interest.