Intermolecular Ordering in Organic Semiconductor Layers and its Correlation to Electronic Properties

This thesis examines the influence of the morphology of organic semiconductors on their electronic properties using analytical transmission electron microscopy (TEM). For the first time, the dielectric properties of organic materials are derived from electron energy loss spectroscopy. A correlation between electron diffraction and current transient measurements of the solution processed polymer poly(3-hexylthiophene) indicates that the semicrystalline structure of the polymer leads to anisotropic charge transport. The study further investigates the structural properties of co-evaporated small molecule blends of fluorinated zincphtalocyanine (F4ZnPc) and fullerene (C60) on different substrates. Energy filtered TEM reveales strong fullerene agglomeration for all substrates considered here, which is shown to be facilitated by an elevated substrate temperature (100°C). These agglomerates are still largely amorphous if the blend is grown on a pristine F4ZnPc layer as required for non-inverted solar cells. However, on an underlying C60-layer, as is typically used for inverted devices, a pronounced order of the fullerene is observed. Device characterization indicates that the highly pure and crystalline C60 domains improve free charge carrier generation and solar cell efficiency. This thesis therefore provides a novel explanation why record efficiencies in small molecule solar cells are only achieved in inverted devices