The Structure-Property Relationships, Degradation Mechanisms, and Building-Integration of Organic Photovoltaic Materials

Abstract

Organic photovoltaics (OPVs) are solar devices where the photoactive materials are made from organic semiconductors. The multitude of organic semiconductors available and the ease by which the properties can be altered via synthetic design makes OPV a highly versatile energy solution. Inexpensive OPV devices are constructed via roll-to-roll printing, can be made flexible and modular, and can have any color and transparency. Due to these advantages, OPVs can be easily integrated into windows, indoor power supplies, and greenhouse systems. However, the technology needs development in a couple critical areas before widescale market adoption can be realized. These limitations include 1) intrinsic material instability, 2) development of interlayer materials for industry-relevant processing techniques, and 3) communication and awareness of the advantages and potential uses of the end products. In this work, we build an understanding of the principles and factors contributing to these limitations through focused analysis of a selection of relevant OPV materials with an emphasis on stability. This dissertation aims to understand the structure-property relationships, degradation mechanisms, and building integration of organic photovoltaic materials. A wide array of experimental techniques are employed to investigate these materials in a cumulative fashion, building from intrinsic material properties as they relate to degradation to addressing the disconnect that limits the real-world marketability of OPV for building-integrated applications. Regarding stability, we demonstrate that materials must be evaluated independently as the active degradation pathways and initiation sites are influenced by unique chemical environments. These intrinsic material instabilities are then joined by other modes of degradation such as microstructure evolution in photoactive layers that necessitate a multimodal analysis for a complete understanding of degradation. Next, we study mechanisms of OPV device enhancement based on the inclusion of two organic cathode interlayers compatible with large area and environmentally friendly fabrication. Finally, the communication barrier between OPV researchers and product adopters is addressed through the promotion of the aesthetic variability and appeal of OPV materials and the construction of an OPV-integrated model building facade that demonstrates a possible application of OPV in built-environments.