Skip to main content
European Commission logo
English English
CORDIS - EU research results

Ultra-high Charge Carrier Mobility to Elucidate Transport Mechanisms in Molecular Semiconductors

Periodic Reporting for period 2 - UHMob (Ultra-high Charge Carrier Mobility to Elucidate Transport Mechanisms in MolecularSemiconductors)

Reporting period: 2021-05-01 to 2023-10-31

Organic electronics is an active field of research that aims to complement silicon with organic semiconductors. The former is energy- and cost-intensive, whereas the latter are cheap to produce and allow additive manufacturing of electronic circuits. The UHMob project objective was twofold. On the one hand, the project aimed to design, synthesise, and assess the performance of a novel generation of organic semiconductors (OSCs) creating a favourable environment for industrial innovations. On the other hand, UHMob delivered the finest quality research training and transfer of knowledge in an interdisciplinary, inter-sectoral, and emerging supra-disciplinary field, to 15 early-stage-researchers (ESRs) to educate them to become future scientific leaders.

After 4,5 years of research, UHMob has achieved its objectives by contributing to advancing the field of organic electronics in developing molecular semiconductors with improved charge transport characteristics for unprecedented industrial applications. It has notably been found that chiral OSCs exhibit a surprisingly large magnetoresistance, allowing organic field effect transistors to be switched on/off by an external magnetic field in addition to the usual electric field, paving the way to a double binary computer logics. The charge carrier mobility, which is the figure of merit of semiconductors, remains on the order of 20 cm2/V.s. Thanks to the elucidation of the charge transport mechanism within organic semiconductors performed by a joint spectroscopic and theoretical study, it is now better understood that it is an intrinsic limitation to this class of materials. The inherent sensitivity of charge transport towards ambient conditions was exploited for fabricating state-of-the-art humidity sensors. UHMob also contributed to the general understanding of polymorphism, i.e. the existence of more than crystal form for a given compound. The results obtained on the crystallization of organic semiconductors are transposable to active pharmaceutical ingredients for which polymorphism often determines the therapeutic action mode. Finally, UHMob has explored the revolutionary concept of the coupling of the energy levels of the molecules with quantized states of vacuum. This concept holds great promise for selectively controlling chemical reactivity by external means and thus offers multiple opportunities for chemical process improvements.

To reach these goals, academic and industrialist research groups from Belgium (ULB, UMONS), UK (UCAM), France (UNISTRA), Austria (TUGRAZ), Germany (BASF, UBER, MPG), Spain (CSIC), Italy (Polycrystalline) and Japan (KU) selected for their scientific and technological excellence in the field, teamed up to form a world-leading consortium to contribute to the research and training programme. UHMob 15 ESRs could thus take part in a total of 150 trainings delivered by the project and their hosted organisations on different transferable skills and technical aspects of their PhD research. Besides, more than 30 secondments were organized, enabling ESRs to learn complementary techniques. In parallel, ESRs presented their research results in numerous conferences and publications ( while additional papers are still being prepared. Finally, ESRs post-graduated since 2022 already joined a research group in their field of research while the majority of ESRs will defend their PhD programme in 2024.
A series of innovative semiconductors was successfully synthesised for the study of the transport of electric charges. Terahertz and microwave photoconductivity measurements were combined with molecular dynamics simulations to demonstrate that transient charge (de)localisation mediated by lattice vibrations imposes an intrinsic limit to charge carrier mobility. These efforts have led to an unprecedented improvement of how charge transport occurs in highly ordered molecular materials. Especially, detailed understanding was gathered on the dual role of phonons, which on the one hand lead to scattering of the charge carriers but on the other hand source dynamic energy disorder and the transient population of spatially delocalized states. This fundamental understanding leads to the important conclusion that OSCs have reached their ultimate properties in terms of charge transport precluding industrial developments. New research directions aim at multifunctional organic semiconductors, for example transporting charge and acting as sensors or showing large magnetoresistance as a result of their chirality. OSCs, absorbing intensely visible light, were studied for the coupling of molecular electronic states with the quantized energy levels of vacuum field. This original concept gains popularity in chemistry because it allows an external control on chemical processes. For a selected set of OSCs, the study of the bulk and surface polymorphism was completed allowing also the isolation of several single crystals. Crystalline structure determination has been achieved by single crystal and powder diffraction measurements. The thermodynamic and kinetic stability of different polymorphs were studied both for bulk material than for thin films. Deposition and characterisation with different techniques were also considered to evaluate the quality and properties of the obtained crystal forms. The understanding of crystallisation mechanism and of polymorphism is particularly relevant for European electronic, chemical and pharmaceutical industries. In total, 39 scientific articles were published within the whole duration of the project, 35 written or co-written by ESRs and openly accessible. PhD theses are also available in open access. Importantly, the ESRs have actively disseminated their research results in more than 48 conferences. One of the main objectives of UHMob was to ensure the training and proper supervision of all ESRs according to their career objectives. For the whole duration of the project, a total of more than 180 ECTS of trainings were delivered to ESRs including secondments. On December 2023, 6 young researchers defended with success their PhD theses. The rest of them will obtain their doctoral diploma in the course of 2024. The MSCA UHMob programme has without any doubt contributed to ESRs’ skills development, enhanced ESRs’ career perspectives and their employability since already 5 of our now post-doctoral researchers have joined a renowned lab or company.
In a concerted research effort, UHMob has contributed to advancing the field of organic electronics by developing molecular semiconductors with improved charge transport characteristics for industrial applications. The project also developed revolutionary concepts, such as the coupling with vacuum states that are widely applicable to control structure and reactivity across chemistry. A fundamental understanding of charge transport mechanisms in organic materials, by an integrated theoretical and experimental approach, has constituted an important achievement, too. Finally, the control of polymorphism of organic compounds which remains an unsolved scientific problem, notably for the pharmaceutical sector, is actively pursued. The largest and most noticeable societal impact of UHMob is the cross-sectorial and interdisciplinary education of 15 young scientists, through research. They will be part of the next scientific elite that Europe needs for its administration, governments, industries, and universities.
UHMob Logo