| Organic photovoltaic (OPV) devices have the potential to be a cost-efficient, clean, and renewable energy source. A fundamental process in OPV devices which directly impacts the device performance is the diffusion length of Coulombically bound electron-hole pairs or excitons. It is therefore important to investigate how chemical structure and processing conditions impact the exciton diffusion length. This study is difficult to perform with the current body of literature since compounds in separate works differ by a number of chemical modifications. Comparisons between works are further complicated by the use of different techniques to measure the exciton diffusion length. To resolve these issues, the first aim of this dissertation is to compare the fabrication, measurement, and analysis procedure for six different techniques to measure exciton diffusion length. We find that bulk quenching techniques are preferred over surface quenching techniques which require elaborate fabrication procedures, multiple measurements, and a number of assumptions in the analysis process. The second aim of this dissertation is to investigate how chemical structure and processing conditions impact the exciton diffusion length. We find that decreasing the conjugation length in a small molecule leads to an enhancement in the exciton diffusion length while replacing the linear alkyl chains with bulky ethyl hexyl groups has no significant effect. Lastly, we show that processing films with a high boiling point solvent leads to an enhancement in the exciton trap density which directly reduces the exciton diffusion length. |
