Undergraduate Thesis Or Project

The Impact of Crystal Morphology on the Opto-Electronic Properties of Amorphous and Organic Crystalline Materials

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  • Organic aggregates and transparent amorphous metals are transforming opto-electronic devices such as highly efficiency solar cells and flexible displays. We present a fundamental optical study of how local morphology critically impacts the device performance of both stacked, conjugated organics and In-Ga-Zn-O (IGZO) transparent metallic materials. Derivatives of anthradithiophene (ADT): ADTTES-F, ADT-TDMS-F, and ADT-TSBS-F were investigated through polarization-dependent optical absorption spectroscopy. While each ADT derivative has a different intermolecular stacking morphology, the intramolecular physics is dominated by their identical conjugated ring structure. We show that the morphology-dependent dipole-moment orientation drastically changes the electronic excited states, through mapping the absorption spectra anisotropy with respect to polarization. Photocells ideally need transparent metals to efficiently harvest the charges created. We present a method of extracting the band gap and Fermi energies for amorphous metals and semiconductors. To determine the Fermi energy and defect bands in such materials we developed a novel simulation code to fit data obtained from a spectroscopic technique called Photo Excited Charge Collection Spectroscopy (PECCS).We applied this technique to amorphous In-Ga-Zn-O (IGZO) transistors, however due to IP protection, we present the procedure through analysis on a simulated device. When applied to a real IGZO device, the code gave realistic values (on the order of eV) for the Fermi energy and optical band gap (Within 0.2 eV).
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