Organic photovoltaics: From materials development to device application

Organic photovoltaics (OPV) are a promising energy source for the future because they have potential advantages over the conventional inorganic PV (silicon based PV), including lightweight, flexibility, and low cost roll to roll production. These advanced properties of organic materials enable future applications with great features, such as OPV on flexible plastic substrates for mobile devices, or solar paints for cars and homes. However, the efficiency of OPV is still low (the best reported efficiency of OPV devices is 9%) compared to inorganic PV (Si-based PV with 15-20% efficiency). The low efficiency of OPV is due to limits of current organic materials and the lack of understanding fundamental processes in OPV under operation. In addition, the OPV devices suffer low stability.;The research presented in this dissertation utilizes both materials design and device optimization to address the limitations of OPVs. In Chapter 3, we present a chemical annealing method used to convert the amorphous films to polycrystalline films and study the effect of morphology change on device performance. In Chapter 4, the synthesis and characterization of organic dyes that undergo symmetry breaking charge transfer are shown. These compounds are expected to have lower exciton binding energies, thus lowering the energy cost for charge separation in OPVs. Chapter 5 covers the energy sensitization of C60 and application in OPVs to improve absorption efficiency. While OPVs with inverted structures have been shown to have improved lifetime, the efficiency of inverted OPVs are often lower than the conventional OPVs. Study on device physics of OPVs with inverted structures in Chapter 6 shed light on the origin of power loss and serves as guidance to design new materials for inverted OPVs.