Applications of Redox Active Molecules in Solid State Electronics Devices and Organic Photovoltaic Cells

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Title: Applications of Redox Active Molecules in Solid State Electronics Devices and Organic Photovoltaic Cells
Author: Chen, Zhong
Advisors: Veena Misra, Committee Chair
Carl Osburn, Committee Member
Michael Escuti, Committee Member
Orlin Velev, Committee Member
Abstract: Redox active molecules have been studied for several years due to their interesting charge storage properties for future application in molecular memory devices with multi-bit low-voltage operation and ultimate scalability. Hybrid Si-Molecular devices with liquid electrolyte as gate contact have been demonstrated for future DRAM and FLASH memories. The focus of this dissertation work has been on developing the completely solid state hybrid Si-Molecular devices embedded with redox active molecules to facilitate ease of integration. In addition, redox active molecules have also been explored in potential application in organic photovoltaic cells. This work exploits the charge storage properties of redox molecules in solid state devices and the absorption profile of the redox polymers. The charge transfer and charge screening process in conventional electrochemical cell with liquid electrolyte has been characterized using cyclic voltammetry measurements. The role of the liquid electrolyte and the electrical double layer in electrochemical cell for the redox process has been discussed. The solid state approach to hybrid Si-Molecular devices has been proposed. The solid state dielectric layer has been considered to replace electrical double layer. The requirements of dielectric layer and deposition methods in solid state molecular memory device are investigated for preservation and characterization of the redox molecules. AlN, Al2O3 and HfO2 are deposited and examined on top of redox active polymers or redox monolayer in metal-insulator-molecules-silicon (MIMS) or metal-insulator-molecules-metal (MIMM) capacitors. The CyV measurements indicate that the redox properties are preserved after dielectric layer deposition on molecules. The leakage of MIMM capacitors has been greatly improved after the optimization on HfO2 atomic layer deposition conditions and the W/WN gate stack. The low leakage current of MIMM structure provide a reliable test platform for redox molecules as well as the other molecule with more functionalities. The redox process in the ionic cell has been modeled with equivalent circuits. The capacitance at different frequencies for EMS capacitors is simulated to study the electrical properties of the solid state molecular device. The frequency dispersion of capacitance measurements for MIMM capacitance has been explored for understanding the redox charging or trapping in the molecular layer. Si nano-membranes are fabricated as an alternative contact to molecules. Solid state molecular transistors are demonstrated for the possible application in FLASH memory. Redox polymers are investigated for the application in renewable energy area. The organic nanoparticles-polymer solar cell has been compared with conventional bulk Si solar cell. The integration of redox polymers helps to improve the absorption profile of active layer in organic solar cells. Organic solar cells with P3HT and PCBM are fabricated and characterized for the future incorporation of redox molecules. In summary, this work provides the fundamental insights and realistic approaches for the applications of redox active molecules with unique charge storage properties into solid state electronic devices and organic photovoltaic cells, which may enable the solutions for the low cost multi-bit low-voltage scalable molecular memories as well as the high efficiency organic solar cell embedded with redox molecules.
Date: 2009-12-08
Degree: PhD
Discipline: Electrical Engineering

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