2013 Theses Doctoral

Processes and Materials for Organic Photovoltaics

Cox, Marshall

The field of organic photovoltaics is driven by the desire for better and cheaper solar cells. While showing much promise, current generations of organic photovoltaic (OPV) devices do not exhibit properties that are suited for wide scale commercialization. While much research has been dedicated towards this goal, more yet needs to be done before it can be clear whether this is an achievable goal. This thesis describes new materials investigations for higher efficiency better stability organic photovoltaics, as well as new processes that broaden the application and fabrication space for these devices. The application of electro-polymerization, a deposition process, towards organic thin-film fabrication is discussed. This novel process for OPVs is followed by an analysis of new and interesting materials for OPV devices, including a higher efficiency hole-transporting material, and two hole-transporting molecules that exhibit self-assembly during OPV fabrication. The results of these investigations indicate the possibility for increased fabrication freedom and control, molecular species design that could allow higher efficiency devices, as well as indications of the role that molecular interactions in OPV heterojunctions play. In addition, the possibilities of integrating graphene, the two-dimensional form of carbon, into OPV architectures is discussed. A new process for graphene transfer that allows the integration of graphene into chemically and physically more fragile systems including those composed of small molecule semiconductors is described and experimentally verified. Graphene is then integrated as a cathode in OPVs, and a modeling and experimental investigation is performed to evaluate the potential for integrating graphene as a recombination layer in tandem OPVs. Based on this investigation, the integration of graphene into tandem OPVs could enable higher efficiency devices and significantly broadened architectural freedom for tandem fabrication.