Quantifying the Spatial Morphology of Organic Films through Polarization-dependent Imaging
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Date
2020
Authors
Scott, Madelyn "Madi" Nicole
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Organic semiconducting materials are appealing, green alternatives to conventional semiconductors because they can be solution-processed into films. However, solution-processing fabrication methods can be prone to morphological disorder, which we define as the variety of sizes and shapes of crystalline structures produced within a single film. A large degree of morphological disorder in semiconducting films inhibits their electronic functionality for use in technological devices. Quantitatively characterizing the mesoscopic crystalline structures, or domains, of organic molecules after film formation from solution enables insight into how macroscopic deposition conditions, like temperature and solution concentration, affect spatial morphology. We constructed a homebuilt microscope to acquire images of films with polarization-dependent transmission. To complement this technique, we also developed an image analysis software package to characterize film morphology. A series of images are collected at a single spatial location on the sample, rotating the polarizer between each image. This process is repeated for several spatial locations on the film surface. For every pixel in the image, the absorption signal as a function of polarization angle is fit to a sinusoidal curve, and the parameters from the best-fit curves are used to create a panoramic image of the entire film surface. Once the panoramic image has been built, the sinusoidal fitting parameters are employed again to assign pixels in the image to discrete aggregate domains within the film. A collection of domain metrics (size and aspect ratio) are computed to describe the morphology of the film after these domain assignments have been made. In this work, several organic films are produced under different deposition temperatures and solution concentrations. The resulting morphologies of these films are compared. This examination provides insight into how the physical properties of organic semiconducting films are affected by macroscopic differences in their formation environments. By better understanding the relationship between deposition conditions and film formation, existing solution-processing techniques can be further controlled and refined to achieve target physical properties in organic semiconducting materials.
Description
76 pages
Keywords
Physical Chemistry, Chemistry, Microscopy, Organic Semiconducting Films, Morphology, Flood Fill Algorithm, TIPS-Pentacene, Polarization-dependent Imaging