Molecular Engineering of Group 14 Phthalocyanines and Their Role in Organic Photovoltaic Devices

Abstract

Organic photovoltaic (OPV) devices utilizing organic (carbon-based) semiconductors have maintained research interest due to their potential for inexpensive, non-toxic, flexible, and lightweight solar modules. Numerous organic polymers and small molecules have been investigated for OPV applications, however a focus on maximizing the power conversion efficiency (PCE) of lab-scale devices has generated many novel active materials that are too complex to be realistically synthesized on a commercial scale. It has become apparent that developing low-cost, scalable, and stable active materials is crucial for the commercialization of OPV devices. Metal phthalocyanines (MPcs) are a well-known family of molecules with established scale up chemistry from their use as colorants and have demonstrated strong performance as low-cost semiconductors in organic electronic devices. However, their potential in solution-processed OPV devices has not been fully realized. In this thesis, a series of materials based on silicon phthalocyanine (SiPc) and tin phthalocyanine (SnPc) were synthesized and characterized. Novel molecular designs and OPV device architectures were investigated to further establish the use MPcs as low-cost active materials and to probe new applications. Specifically, the chemical and physical differences of structurally analogous soluble SiPc and SnPc derivatives were examined for the first time. The ability of a SiPc derivative to act as a thermal crosslinker to stabilize active layer morphology while simultaneously contributing to photocurrent generation was also proven. SiPc derivatives were then studied as electron acceptors paired with P3HT and PBDB-T donor polymers, achieving a PCE up to 4.3 %. The results herein establish new potential roles for group 14 MPcs in OPV devices while also demonstrating their synthetic simplicity and versatility. This work also serves as a basis for the wealth of chemical functionalization which remains available for continued optimization of these materials.