Correlation between Structural Properties and Intermolecular Coupling in Molecular Donor/Acceptor Thin Film Heterostructures

Abstract

Charge transfer (CT) states coupled to the electronic ground state of a donor molecule mediate charge carrier generation and recombination processes, which are crucial for organic photovoltaic (OPV) devices. In this thesis, mixing behavior and intermolecular coupling of donor (D) and acceptor (A) molecules in thin films prepared by organic molecular beam deposition (OMBD) are investigated. As the donor materials, diindenoperylene (DIP) and pentacene (PEN) and, as the acceptor materials, perylene diimide derivatives (PDIR-CN2 and PDIF-CN2) are used. A steric shielding effect of the acceptors´ side chains on the intermolecular interaction between the perylene diimide backbones is examined with real-time X-ray diffraction and optical measurements. As a model case the CT effect in DIP:PDIR-CN2 system is studied in details. The correlation between the intermolecular interactions, the structural properties within a film, the ground and excited state electronic structure, and the behavior of electronic devices based on CT is discussed. The comparison between all four D/A systems shows a direct correlation between small molecule compatibility and the CT properties of the corresponding D/A complex. The sterical, structural, and energetical factors are analyzed.