Enhancing the Dielectric Constant of Organic Materials

When a solar cell absorb sunlight, an excited state is formed, which consists of a positive and a negative charge. These charges need to be separated from each other, to prevent them from recombining, and to make them flow through an external circuit in order to use the electrical energy. Within organic materials, these charges are strongly bound together, which happens because organic materials have a low dielectric constant. In these materials, the positive and negative charges generally only exist for very short amounts of times (nanoseconds) before recombining. In this thesis we present work that can be divided into two categories. The first is focused on improving organic solar cells. We try to synthesize new materials that have a higher dielectric constant, and thus a longer time before the charges recombine. The approach we used is adding functional groups that are more polarizable, or have higher dipole moments. In the second half of the thesis we focus on the method of measuring the dielectric constant of organic materials. We use a technique called impedance spectroscopy, for which we make a capacitor with our materials as a dielectric, and measure its capacitance. The roughness of the films has a big effect on the measured values. The top contact can be formed either through deposition of aluminum, or what we introduce in this thesis, by using eutectic gallium indium (EGaIn), a non-Newtonian liquid metal. The EGaIn top contact has been shown to give more reliable results.