Search for Electron-Deficient Semiconducting Polymers to Rival Fullerenes Luping Yu, University of Chicago, DMR a b This project is aimed at developing novel electron deficient polymers that can be used to prepare all– polymer solar cells exhibiting high efficiency and low cost for solar energy conversion to electricity. We have developed two kinds of new n-type monomers that allow syntheses of numerous new n- type semiconducting polymers (Figure 1). These polymers exhibited a range of energy levels to match solar spectrum. These polymers are being used to develop new solar cells and investigate the structure/property relationship. Another significant development is our discovery of the cooperative effect of plasmonic enhancement on polymer solar cells. It was found that when mixed silver and gold nanoparticles are incorporated into anode buffer layer, the light absorption and hole transport in the polymer layer were enhanced due to plasmonic effect of metallic nanoparticles. The plasmonic effect associated with the dual nanostructures also helps to generate more charge carriers. All of these effects helped to increase the solar energy conversion efficiency and led to a 20% enhancement in solar cell conversion efficiency from 7.3% to 8.7%. Figure 1. Synthesized electron accepting polymers containing a) amide or b) malononitrile functionalities. Figure 2. HOMO and LUMO energy levels of polymers. Figure 3. Current-voltage characteristics of solar cells with and without NPs in PTB7/PCBM system. Nano letters 13 (1), 59-64

Educational outreach and diversity: The Yu group have participated in the Leadership Alliance by offering summer research opportunities in the lab to those from under-represented minority groups. We have succeeded in recruiting a minority undergraduate student (Kevin Trujillo, Hispanic) from Loyola University to join us for the summer research. He is working on a project to characterize new polymers for solar cells. He is enjoying the research in our lab and gaining experience. Our group is also hosting the summer research by a minority high school student (Carah Alexander) and a international REW student from Zhejiang University of China. They have started the training in fabrication of organic solar cell devices and measurement of Current density-voltage (J-V) characteristics. Numerous interesting data have been collected. They are now in the process learning how to analyze them. Outreach: The PI has succeeded in establishing more collaborations with several companies, including Solarmer Energy for solar cell devices, Zhejiang Pharmas. The companies all offered financial support and technical assistance for this project. In the past three years, the PI enjoys close collaborations with several research groups and national and industrial labs: Prof. Tobin J. Marks at Northwest University on device fabrication and characterization; Dr. Lin Chen at Argonne National Lab (ANL) on electronic dynamics of low band gap polymers; Professor Yang Yang at UCLA on Inverted solar cells; Dr. Hieke Riel at IBM labs at Zurich, Dr. Dean M. DeLongchamp (NIST), Prof. N. J. Tao at Arizona State University on molecular electronics. All of these collaborations resulted in publications in highly respected journals. An important collaboration with Hong Kong University on organic electronic materials is undergoing. Prof. Yu is guiding two minority students (Kevin and Carah) for the summer research on photovoltaic devices by using the new polymers developed in the group. Search for Electron-Deficient Semiconducting Polymers to Rival Fullerenes Luping Yu, University of Chicago, DMR