New Conjugated Polymer Photovoltaic Materials Design And Performance Study

Solar energy is the most abundant, renewable, and clean energy on the earth.Cheap production of electricity from solar energy is one of the top challenges today. Asa potential alternative to silicon-based photovoltaic cells, polymer solar cells hasgenerated significant interest because of their low cost, light weight, and machanicalflexibility for large-area roll-to-roll coating process. The state-of-the-artbulk-heterojunction (BHJ) solar cells are generally composed of a transparent anode,such as ITO, an anode buffer layer, such aspoly(styrenesulfonate)/poly(3,4-ethylendioxythiophene) (PSS/PEDOT), an active layercontaining a polymer donor, such as poly(3-hexylthiophene) (P3HT) and a fullereneacceptor, such as [6,6]-phenyl C61butyric acid methyl ester (PC61BM) or [6,6]-phenylC71butyric acid methyl ester (PC71BM) , and a metal cathode, such as Al. The powerconversion efficiency (PCE) of P3HT/PC61BM-based solar cell has reached about4~5% .The efficience of the polymer solar cells reported in the papers have reached 7-8%now, but the PCE and the stability of polymer solar cells are still too low to be widelyused in our society life. The present paper focused on the design, synthesis and theoptimization of the conjugated polymers.In Chapter 1, the principle and the brief history of the organic polymer solar cellsand some typical materials are discussed.In Chapter 2, a new acceptor unit, 2-alkyl-thieno[3,4-b]imidazole, was synthesizedthrough an annulation reaction between a 3,4-diaminothiophene derivative and acarboxyl acid or an acyl chloride and was used for synthesis of Donor-Acceptorconjugated copolymers. Copolymerization of 2-alkyl-thieno[3,4-b]imidazole andbenzo[1,2-b;3,4-b′]dithiophene (BDT) or dithieno[3,2-b:2′,3′-d]silole (DTS) afforded 6new low bandgap polymers. These polymers were firstly applied in polymer solar cells.The best 0.72% efficiency was obtained from the P2/PC71BM blend by the dip-coatingmethod.In Chapter 3, benzotriazole unit was chosen to be optimized. Given the electronegativity of the N atom and the intramolecule hydrogen bond, pyrrole wasintroduced to the polymer back-bone. In addition, some attempts to expand theconjugation of the bnezotriazole itself had been made.