Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - ICONICAL (In control of exciton and charge dynamics in molecular crystals)

Teaser

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...

Summary

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

In the first 18 months substantial progress has ben made on several front in this project:
- theoretical studies of optimal crystals structures for specific processes
- synthesis of new materials with desired properties
- initial measurement on exciton diffusion in these materials

Final results

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. No socio-economical or wider societal implications have merged from the project so far.