Undergraduate Thesis Or Project
 

Modeling optical reflection and electric field intensity in organic semiconductor microcavities

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https://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/sx61dv12f

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  • Organic semiconductors are a promising alternative to the traditional inorganic semiconductors, such as silicon. Organics are solution-processable, low-cost, sustainable, and have interesting optoelectronic properties. One such property is the formation of exciton-polaritons, quantum quasi-particles formed by an electron-hole pair in the semiconductor and a photon. This process can be induced by placing the organic semiconducting material in an optical microcavity, which has mirrors on either side of the material. The electric field distribution within the cavity, as well as other properties such as the device’s overall reflectance, can be used to analyze this interaction. The photon-exciton coupling can enhance device performance by reducing degradation, so it is desirable to optimize the cavities in order to maximize this coupling strength. In this thesis, I compare electric field distributions within a variety of cavity structures and under a variety of conditions. I show how these cavities can be optimized for TIPS-Tc, a benchmark organic semiconductor. I focused on three different microcavity designs. The first used silver mirrors on either side, the second used a silver mirror on one side and a distributed Bragg reflector (DBR) on the other, and the third used DBRs on either side. Each system was simulated, along with a variety of control systems, to determine how the electric field distribution and reflectance was impacted by the angle of incidence, wavelength and polarization of the incident light. From these observations, the thickness of the semiconductor layer was altered to optimize the hybrid and all-DBR cavities for wavelengths near 532 nm. The tester material was then replaced with TIPS-Tc to analyze the strength of the light-matter coupling in the original and optimized cavity designs. All simulations were performed in Python 3.11.1, using the transfer matrix method. The results of the simulations indicated that the electric field distribution changed depending on the mirrors used, and thus a single thickness of the TIPS-Tc layer did not optimize every cavity structure. Using the shape of the electric field distribution functions for hybrid and DBR cavities in comparison with the all-metal cavity, we determined that by increasing the thickness of the semiconductor layer, we could optimize the hybrid and all-DBR cavities. Comparing these new cavity designs with the originals, we found evidence of strong coupling in the optimized cavities but not in the originals. The results indicate that all three cavity designs have the potential to induce strong coupling and highlight the need for numerical optimization of each cavity structure prior to fabrication.
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