Low Band-Gap Conjugated Polymers for Plastic Solar Cells

Doctoral thesis, 2007

Today, fossil fuels like coal, oil, and natural gas are used for more than 60% of the world's electricity production. These fuels have a very negative impact on the environment and many researchers agree that the earth's climate is changing as a consequence of fossil fuel emissions. There are several examples of more environmentally friendly ways to produce electricity like bio fuels, hydroelectric power, wind power, and solar energy but for the fossil fuels to be totally replaced, the alternatives must be cost effective, robust, and long lived. Direct conversion of sunlight to electrical energy in solar cells is a very eco-friendly method of generating electricity. Traditional silicon based solar cells have been used in commercial products for a few decades but there are other promising solutions. For instance, polymer based solar cells could be manufactured in cheaper, less complicated, and less energy consuming processes. Design, synthesis, and evaluation of conjugated polymers for solar cells are described. The focus has been on realizing polymers which can absorb light at long wavelengths and convert it into electrical energy. For long wavelength light to be absorbed, the polymer must have a low band-gap which is achieved by introducing so called low band-gap segments. The thesis describes the development of these low band-gap polymers in detail and results from solar cell measurements are given. Unprecedented photovoltaic responses at long wavelengths have been reached and some of the materials presented herein display very promising efficiencies.