Doctor of Philosophy (PhD)
Organic semiconducting polymer thin films are core materials for organic electronics that are conventionally prepared by solution processing techniques. Despite having the advantage of easy and fast thin film manufacturing, solution techniques have intrinsic drawbacks, such as disordered and poor molecular organization in the film (often resulting in poor device performance), as well as insufficient stabilities of the films and resulting devices. To improve this situation, we designed a novel “bottom-up” fabrication of surface-immobilized organic semiconducting thin films through in situ polymerization. This new strategy will allow high degree of control over molecular organization which therefore results in improved free charge carrier transport efficiency. An additional benefit of this strategy will be the enhanced stability of thin films due to covalent attachment of the resulting conducting polymers to the surface. Initially, we developed an approach towards deposition of surface-bound semiconducting polymer thin films via in situ electropolymerization. When the resulting thin films were used as hole transporting materials in photovoltaic devices, they demonstrated enhanced photocurrent generation quantum efficiencies and remarkable stabilities as compared to conventional spin- casted thin films. Based on the promising results from this initial attempts, a chemical surface-initiated in situ polymerization based on Ni catalyst transfer living Kumada polycondensation was developed using highly efficient Ni(II) external catalytic initiator. Thin polythiophene films with improved surface morphologies were successfully grafted on substrates after systematic optimization of the experimental conditions. As an important extension of this strategy, we also prepared nanopatterned surface-immobilized polythiophene thin films as a hole transporting counterpart of the ideal heterostructures for bulk-heterojunction type organic photovoltaic devices. In a parallel study, surface-immobilized semiconducting polymer thin films were prepared by stepwise surface-initiated in situ polymerization using highly efficient Cu-catalyzed alkyne-azide cycloaddition (click) reaction. In this project, we found that stepwise preparation of semiconducting polymer thin films not only promises complete control over surface morphology, thickness, and molecular composition of the resulting polymer films but also allows building complex copolymer thin films with desired photophysical properties. Taken together, those three methods represent a powerful “bottom-up” alternative to the traditional methods of preparation of semiconducting polymer thin films.
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Hwang, Euiyong, "Surface-initiated Polymerization as a Novel Strategy towards Preparation of Organic Semiconducting Polymer Thin Films" (2011). LSU Doctoral Dissertations. 2850.
Nesterov, Evgueni E.