Heterojunction Solar Cells Using Chemically co-doped Titania Nanotube Arrays for Simultaneous Light Absorption and Carrier Transport Hao Zeng, SUNY at Buffalo, DMR Titanium dioxide (TiO 2 ) is an important material for solar energy applications, e.g., dye-sensitized solar cell and photoelectrochemical water splitting, mainly because of its chemical stability in aqueous solution. The electronic property of TiO 2, however, is not well suited for such applications. Particularly, its band gap (3.0 eV in the rutile phase and 3.2 eV in the anatase phase) is too large for optimally absorbing sun light. We have proposed a novel approach, named chemical co-doping, to reduce TiO 2 band gap. In this approach, codopants such as (N, P) could form strong chemical bonds even though they both occupy anion lattice sites. The strong bonding could lower their formation energy and enhance the doping concentration. The results from our solution-based synthesis indicate the success of chemical co-doping. Significant band gap reduction has been achieved. This work represents one of a few successful doping schemes to reduce the band gap of TiO 2 to the visible region. (Top) SEM images of (N, P) co-doped TiO 2 nanoparticles; (Bottom) Scanning tunneling spectroscopy of co-doped TiO 2 showing band gap reduction from 3.2 to eV. Inset shows a possible structure of the codopants. Ti O P N

In the past summer, Mrs. Dianne Link from South Park High School worked with graduate student Jim Parry at UB to develop new labs and hands on activities that will be used in her classes. The specific theme is renewable energy. She will be using a lab/demonstration kit in her classes this coming year. This kit contains a regular Si and a thin film Si solar cell with software to monitor photovoltaic performance. To better instruct the students we covered the physics, variety of uses, and how technical and research innovations are pushing solar technology. The physics of solar cells covered included absorption of sunlight, P-N junctions, and important physical properties and measurements. The high school students will be able to see direct I-V measurements and how those measurements change with varying illumination. The variety of solar cell materials and production will be introduced by discussing the two different cells that are included in the kit. Mrs. Link also saw examples of other thin film and dye sensitized solar cells. The use of different solar cells leads to further topics including solar materials and areas of research and innovation. In the classroom Mrs. Link will also be able to use online resources for real-time tracking solar energy arrays on houses and businesses in New York. Last winter, co-PIs Sun and Zhang outreached researchers at IBM and established a working relationship with Dr. David Mitzi and others at IBM Watson Research Center on the study of earth-abundant copper zinc tin selenide solar cell materials. A second visit is due at anytime. Heterojunction Solar Cells Using Chemically co-doped Titania Nanotube Arrays for Simultaneous Light Absorption and Carrier Transport Hao Zeng, SUNY at Buffalo, DMR