TECTESA · Tuning Exciton diffusion through Charge-Transfer Excitations in Supramolecular Assemblies

Tuning Exciton diffusion through Charge-Transfer Excitations in Supramolecular Assemblies

The transition toward a sustainable, low-carbon economy is a central priority of the European Union, as reflected in the European Green Deal and Horizon Europe’s objectives for clean energy and advanced materials. Meeting these goals requires the development of innovative materials capable of efficiently harvesting and converting solar energy while remaining cost-effective and environmentally friendly. In this context, organic materials have emerged as a promising alternative to traditional inorganic semiconductors. They can be processed at low temperatures, are lightweight and flexible, and allow for chemical tailoring of their properties, making them ideal for next-generation photovoltaic and optoelectronic technologies such as organic solar cells and light-emitting diodes. Despite this promise, the performance of organic-based devices still lags behind inorganic counterparts. A key limitation lies in the incomplete understanding of how energy and charge are transported within these materials. Organic semiconductors are composed of discrete molecules bound by weak non-covalent interactions, which means that their electronic states are often localized and strongly coupled to molecular vibrations and structural disorder. Unlike crystalline inorganic solids, where electrons move freely through periodic lattices, transport in organic systems is inherently dynamic and influenced by molecular motion. This complexity makes it difficult to predict or optimize the efficiency of energy and charge migration, which directly affects device performance. Addressing this gap requires a theoretical framework capable of linking molecular structure and organization to the macroscopic properties observed experimentally. The TECTESA project (Theoretical Characterization of Energy and Charge Transport in Supramolecular Aggregates) was designed to tackle this fundamental challenge. Its overarching goal was to provide a unified theoretical understanding of excitonic and charge transport in organic materials by identifying how structural and electronic parameters control energy migration and optical response. Through the study of representative organic crystals and supramolecular aggregates, the project aimed to establish general design principles that guide the development of materials with enhanced transport properties. TECTESA builds upon the recognition that excitons — bound electron-hole pairs generated upon light absorption — play a central role in the operation of organic devices. Their ability to migrate efficiently determines the performance of solar cells, light-emitting devices, and other optoelectronic components. However, exciton transport depends sensitively on the degree of electronic coupling between molecules, the presence of dynamic disorder, and the strength of vibronic interactions. Understanding how these factors interact requires simulations and theoretical analyses that capture the balance between electronic delocalization and vibrational effects. The project addressed this challenge by employing atomistic and semiclassical models to investigate how microscopic features — such as molecular packing, electronic couplings, and vibrational reorganization energies — influence exciton mobility and optical spectra. By systematically exploring a broad range of conditions, TECTESA aimed to identify the transition regimes between coherent, incoherent, and mixed transport behavior, and to define the structural motifs that promote efficient energy transfer. These insights enable the formulation of general rules that can be applied across different families of organic materials, extending beyond specific chemical systems to provide predictive guidelines for molecular design. Ultimately, the project provides not only new scientific insights but also a conceptual framework to guide future research. By elucidating the key parameters governing exciton and charge migration, TECTESA contributes to the rational design of materials that can accelerate Europe’s transition toward sustainable and high-performance optoelectronic technologies.

Data: CORDIS, © European Union