Investigation of the Effect of Antenna Molecules onto the Conjugated Polymer Based Photovoltaic Cells

The fundamental aim of this research work is to do basic research leading to the development of efficient plastic solar cells. The need for alternative energy resources in the world is clear, and harvesting energy directly from the sun is an obvious direction of research. Solar cells based on silicon and other inorganic semiconductors have made significant progress in the last several decades, however their high cost remains an obstacle to large-scale use. Plastic solar cells, made from organic, carbon-containing polymers, may provide an inexpensive alternative. Plastic solar cells utilize the same basic photophysics as natural photosynthesis, although the molecules and structures than can be fabricated in the Laboratory are much simpler than those that have evolved in nature. Organic materials provide a virtually unlimited variety of molecules with different electronic, optical, and material properties that can be tuned for a specific device purpose. A new field of technology based on these organic materials shows promise to be cost effective and reliable enough for commercial development. The plastic solar cell harvests energy from sunlight by the following sequence of steps: 1) light is absorbed to create an excited state molecule, 2) the excited state molecule is separated into mobile charges, 3) the mobile charges are transported out of the device and delivered to the external circuit. Recently, the most efficient plastic solar cells have been designed with a mixture of different molecules, each tuned to perform particular functions. One technical hurdle to obtaining efficient plastic solar cells is that the velocity with which charge is transported in organic materials is typically much lower than in inorganic materials. This limits the thickness of the device, which therefore limits the amount of light that is absorbed. Designing new materials with higher velocities of charge transport is fundamentally difficult or impossible. However, the amount of light that is absorbed by the device can be increased by adding additional molecules into the mixture. These molecules harvest the incoming light energy and transfer it to different molecules where the charge separation can take place. Chlorophyll, the light-harvesting center in plants, operates on the same principle, called the antenna effect. The specific aim of this research work is to investigate a variety of molecular systems and identify those that can function as antenna molecules in the plastic solar cell. Adding these molecules into the plastic solar cell mixture can increase the amount of light that is absorbed and therefore increasing the light-harvesting efficiency.