Singlet Exciton Diffusion in Conjugated Polymers: Relaxation and Thermal Activation

• Applicant: Professor Dr. Carsten Deibel
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449532543

The diffusion of singlet excitons, the primary photoexcited species in organic semiconductors, plays a central role in the performance of organic light emitting diodes and photovoltaics, respectively. Using confocal photoluminescence spectroscopy, our goal is to understand the thermal activation of exciton lifetime and exciton diffusion coefficients in a range of different systems relevant for solar cells with spatial resolution in the sub-micrometer range. In particular, we want to study:• the influence of homocoupling defects and molecular weight in the conjugated polymer PCDTBT with focus on thermal activation• the different characteristics of exciton diffusion within different sized domains and their boundaries by controlling the spherulite growth in P3HT with solvent vapour annealing• how novel non-fullerene acceptors in organic solar cells affect exciton diffusion and the related power conversion efficiency by comparing the impact of energetic differences of polymer–fullerene to polymer–non-fullerene in bulk heterojunction films• how the effective Förster-radius for such systems can be determined by a combination of experiments and simulationsWe will employ the bulk quenching technique by a low, varying amount of photoluminescence quencher blended into the materials of interest as starting point. As this method might have an undesired influence on spherulite growth during solvent vapour annealing, we will also establish the determination of exciton diffusion by singlet–singlet annihilation by confocal fluorescence microscopy, which does not require quenchers. Supported by kinetic Monte Carlo simulations, our combined approach allows us to determine local exciton lifetimes and diffusion coefficients on the sub-micron scale.

• DFG Programme: Research Grants