Synthesis of Conjugated Polymers for Solar Cell Applications

Licentiatavhandling, 2010

Fossil fuels are largely used as a source of energy to fulfil the energy demand of mankind. However, fossil fuels suffer from limitations. The unlimited burning of fossil fuels releases greenhouse gases and causes environmental pollution. Fossil fuels are also an unreliable source of energy since the natural deposit is limited. Therefore, a clean and reliable source of energy is highly demanded. Direct conversion of the solar energy into electrical energy by solar cell technology is clean and desired. Inorganic materials like silicon are still the most widely used for making solar cell devices. Preparation of large area devices from inorganic materials, however, is not easy and therefore it is not possible to produce very cheap solar cells. In 1977, it was observed for the first time that conjugated polymers can conduct electricity. Following this break through discovery, many conjugated polymers were synthesised and characterised for optoelectronic application. In this study, three polymers namely APFO-Black 1, APFO-Black 2 and APFO-25 were synthesised and characterised. The synthesis of the polymers started from simple commercially available materials and the corresponding monomers were built in a step-by-step fashion. The respective monomers were joined to a functionalized fluorene unit by Suzuki coupling methodology. The black polymers showed wider optical absorption and a better match with the emission spectrum of the sun compared to most conjugated polymers. The best device efficiency obtained from APFO-Black 1 was 1.15% while APFO-Black 2 showed an efficiency of 1.49%. APFO-25 on the other hand consists of a polar group to get an improved miscibility and also to get stable nano-morphology of the donor-acceptor blend in bulk heterojunction solar cell device. APFO-25 showed a decent efficiency reaching 2.8%.