In control of exciton and charge dynamics in molecular crystals

Project Information

ICONICAL

Grant agreement ID: 648433

DOI

10.3030/648433

Project closed

EC signature date 28 May 2015

Start date 1 June 2015

End date 31 May 2020

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 000 000,00

EU contribution

€ 2 000 000,00

Coordinated by

TECHNISCHE UNIVERSITEIT DELFT
Netherlands

Periodic Reporting for period 4 - ICONICAL (In control of exciton and charge dynamics in molecular crystals)

Reporting period: 2019-12-01 to 2020-05-31

Summary of the context and overall objectives of the project

It is the aim of the work proposed here to achieve control over charge and excited state dynamics in organic crystalline materials and in this way to come to solid state materials with explicit built-in functionality. The charge and excited state dynamics do not only depend on the properties of individual molecules but are to a large extent determined by the interactions between multiple molecules. By careful engineering of the properties of individual molecules and of the way they aggregate in the solid state crystalline materials it is in principle possible to design materials that exhibit a specific functionality. Examples of this are materials that are optimized to give high charge carrier mobilities and high exciton diffusion coefficients. Both of these properties are of direct relevance for electronic devices based on these materials, such as photovoltaic cells and light-emitting diodes. It is also possible to design more complex functionality in these materials. A first example of this is singlet exciton fission, a process by which one singlet excited state transforms into a combination of two triplet states. This spin-allowed process is of considerable interest in organic photovoltaics since it can in principle increase the maximum thermodynamic efficiency by a factor 1.5. A second example of complex functionality is upconversion of low energy photons into higher energy photons. This is possible by combining two low-energy triplet excited states into a single singlet excited state by triplet-triplet annihilation. The latter is the reverse process of singlet exciton fission.

A successful implementation of these ideas can lead to a substantial improvement in the efficiency of solar cells based on organic materials and more efficient organic electron devices. This will benefit society in terms of a cleaner generation of electricity and more energy-efficient devices.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During this project we have made significant progress in control the opto-electronic properties of crystalline materials. During the 5 years of the project we have:
- unraveled the relation between solid state packing and the charge transport properties
- obtained significant new insight in the mechanism of singlet fission andd the relation between molecular structure and solid state packing and the efficiency of singlet fission
- achieved a theoretically proposed new device structure for photo-chemical upconversion of red photons followed by direct extraction of electrons
- established a new research direction involving the incorporation of large conjugated organic chromophores into 2D pervoskite structures. This has uncovered many new interesting directions to incorporate new functionality in these materials.
The research has led to the publication of over 30 peer-reviewed scientific papers, several of them in high-impact journals. Several publications on the final results are still in preparation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The work in the project has led to several publications in high impact journal such as Nature Chemistry and Nature Materials. These contribution are clearly pushing the boundaries of knowledge in design and characterisation of solar cell materials. In addition, during the project we have significantly expanded the scope by also studying hybrid organic/inorganic pervskite materials with a specific focus on materials where the organic part is key in determining the properties. We have been able to define clear guidelines related to the incorporation of large conjugated organic molecules, which are the key subject of the project, into hybrid perovskite materials and in this way introduce new properties. No socio-economical or wider societal implications have emerged from the project so far.

Mechanism of singlet fission in crystalline materials