Synthesis and characterization of electronic materials for photovoltaic applications

Mejia, Michelle Leann
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Electronic materials are of great interest for use in photovoltaics, sensors, light-emitting diodes, and molecular electronics. Hybrid Inorganic/Organic materials have been studied for device application due to their unique electronic properties. These properties result from the formation of bulk heterojunctions between inorganic (n-type) and organic (p-type) materials. However, due to incomplete pathways for charge transport and poor interfaces between materials, charge trapping and exciton recombination is often high. In an effort to alleviate these problems, we have developed an approach to fabricate bulk heterojunction materials via a seeded growth process. Electropolymerizable Schiff base complexes have been designed, synthesized, and utilized as precursors for conducting metallopolymers. The embedded metal centers are used as seed points for direct growth of size-controllable semiconductor nanoparticles within the polymer film leading to direct electronic communication between the two materials. The synthesis of CdS, CdSe, Ga₂S₃, CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, CuGa[subscript x]In[subscript x]-₁S₂, and CuGa[subscript x]In[subscript x]-₁Se₂ has been seen through TEM and EDX. Devices have been fabricated and current studies have focused on the photovoltaic characterization of these materials which have a PCE of 0.11%. As a second but closely related area, polymers have also been studied as organic semiconductors for device applications. However they are hard to process from solution and their polymeric structure can vary. Both of these problems can be solved by using well-defined solution processable oligomers. Thiophene oligomers have been synthesized and characterized through Single Crystal X-Ray Crystallography, Four Point Probe Conductivity, and Powder Diffraction. These oligomers have a well-defined structure and are solution processable from a variety of solvents which can then be used as models to predict and study the properties of polythiophene.