1. The determining factor for overall perform- ance of polymer solar cells is the property of semiconducting polymer. To develop better materials, a series of new semiconducting polymers with alternating thieno[3,4- b]thiophene and benzodithiophene units was synthesized. It was found that the physical properties of these polymers can be finely tuned for photovoltaic application. The HOMO energy levels of the polymer was lowered by substituting alkoxy side chains to the less electron donating alkyl chains in PTB3 or introducing electron withdrawing fluorine atom into the polymer backbone in PTB4, leading to a significant increase in Voc (28%) for polymer solar cells. The improvement in polymer’s hole mobility and the miscibility with fulleride resulted in power conversion efficiencies over 6% in solar cells based on fluorinated PTB4/PC 61 BM and PTB4/PC 71 BM composite films prepared from mixed solvents, which are among the highest for polymer solar cells. High Efficient Solar Cell Polymers Developed via Fine-tuning Structural and Electronic Properties Luping Yu, University of Chicago, DMR 0703274 Figure 1. Structure and energy level of the polymers. Figure 2. Current – voltage characteristics under AM 1.5 condition (100mW/cm 2 ) of (a)polymer/PC 61 BM solar cells, and (b) PTB4/PC 61 BM and PTB4/PC 71 BM prepared from mixed solvents dichloroben-zene/diiodooctance (97/3, v/v) and (c) EQE spectra.

2. Education: Under this grant, two students- Shengwen Yuan and Youngu Lee have received their Ph. D. degree. Another student, Yongye Liang, is preparing his thesis and will defend it this August. A female graduate student, Hae- Jun Son, and a minority student, Brian Carlsten, are working in this project. One post-doctoral scientist, Dr. Aurélien Gasnier, has joined this project. A female undergraduate student, Ray Claire, is also involved in this project. Journal of the American Chemical Society (2009), 131(22), 7792-7799. Outreach: The success of our new semiconducting polymers has attracted wide interest in collaboration. The PI has established close collaboration with a start-up company- Solarmer Energy Inc. for solar cell devices based on materials developed in PI’s lab (Dr. Gang Li). The company has offered financial support for this project. A patent is filed and is licensed by the Solarmer Energy Inc. The PI also enjoys close collaborations with several research groups and national and industrial labs: Prof. Yang Yang at UCLA on device fabrication and characterization; Dr. Lin Chen at Argonne National Lab (ANL) on electronic dynamics of low band gap polymers; Dr. Hieke Riel at IBM labs at Zurich, Prof. Ivan Oleynik at U. of South Florida on theoretical studies, Prof. N. J. Tao at Arizona State University on molecular electronics; Dr. D.J. Liu at ANL on hydrogen storage polymers, Professors Michael R. Wasielewski and Tobin Marks at Northwestern University, Professor Bin Hu at University of Tennessee and Professor Ricardo Izquierdo at Université du québec à montreal on Solar Energy. Joint publications were submitted or are in preparation. High Efficient Solar Cell Polymers Developed via Fine-tuning Structural and Electronic Properties Luping Yu, University of Chicago, DMR 0703274