STUDY OF MAGNETO-OPTICAL BEHAVIORS AT A FERROMAGNETIC/ORGANIC SEMICONDUCTOR INTERFACE

Organic materials have been widely studied for the last 20 years to use for photovoltaic applications. Organic photovoltaic materials have shown promising properties for solar cells, such as very low cost, flexibility, easy fabrication methods, etc. Although power conversion efficiencies for organic-based solar cells have exponentially grown in the last decade, up to about 13% in early 2016, it is still optimal to increase these efficiencies. In order to raise efficiencies, it is important to study the fundamental mechanisms inside organic materials that lead to photovoltaic properties. This thesis reports the magneto-optical effects on the p-type organic semiconductor, tetracene, from a ferromagnetic/semiconductor interface between thin films of cobalt and tetracene. Magnetic field effect measurements were used to study singlet fission inside tetracene and effects from cobalt on singlet fission in tetracene. When a thin layer of cobalt was added, two main effects were determined. Magnetophotoluminescence results gave evidence of spin interactions at the interface causing spin polarization at the surface of tetracene, reducing hyperfine interactions and increasing the density of inter-triplet states, resulting in net increases in singlet fission. Photoluminescence and absorption results gave evidence of electrical interactions at the interface causing electrical polarization at the surface of tetracene, increasing the electron phonon coupling of tetracene as well as quenching photoluminescence. It is proposed that these changes from the ferromagnetic/organic semiconducting interface can be furthered utilized in photovoltaic and transistor applications based on singlet fission materials and possibly other similar types of organic material-based devices.