This award on solar energy research is co-funded by the Divisions of Chemistry, Materials Research, and Mathematical Sciences of the Directorate for Mathematical and Physical Sciences. A collaboration of chemistry, materials science, mathematics, physics, and engineering groups at the University of Michigan and the University of Southern California will develop a unique, new, thin film solar cell based on polymer-wrapped carbon nanotubes (CNTs). These films will be used in donor-acceptor heterojunctions employing a range of new organic materials and device structures, including polymers and small molecules. The use of CNTs extends the optical sensitivity from the blue into the near infrared, allowing organic-based devices to approach nearly thermodynamically-limited power conversion efficiencies. Simulated excited state (exciton) flow and charge transport through the CNT network uses new treecode algorithms and semi-classical hydrodynamical models. Efficient, multi-dimensional optimization methods are used to develop novel aperiodic dielectric stacks that couple the broad solar spectrum into very thin films used as the active device region in solar cells. A diverse range of undergraduate and graduate students and postdoctoral fellows are engaged in this interdisciplinary research in renewable energy. These students are provided with opportunities to influence policy decisions regarding energy choices through coursework in energy policy and geopolitics on their respective university campuses. The group is also involved in the University of Michigan's Saturday Morning Physics lecture series, providing the public with insights into the latest science and technologies.
In this program our team: Generated a family of p-extended porphyrin compounds that have strong absorption to 1000 nm. These materials were incorporated into photovoltaic cells and showed photocurrent generation to > 900 nm. The synthesis is a very general one and was used to prepare several different complexes. Investigated the interaction of p-extended porphyrins with single walled carbon nanotubes (SWNT). The complexes bind very strongly to SWNT and show rapid photoinduced electron transfer. Investigated the use of chemical annealing (CE) to modify thin film structure and solar cell performance. In the CE process a thin film is exposed to a compound in the vapor phase that binds to the molecules in the film and modifies the morphology of the resulting composite film. The end result is a crystalline thin film. This process led to an increase in current, but a decrease in cell voltage. Investigated inverted solar cell architectures for small molecule based OPVs. We found that ALD deposited ZnO can transform an ITO cathode into an effective anode for the solar cell. Optical field modeling illustrates that the inverted structure is poor with respect to red light collection. Investigated the charge transfer processes in organic heterojunctions, and toward the end of the program this work was extended to organic/inorganic heterojunctions. Technology transfer was a significant outcome of our work. We had 5 invention disclosures. Patent applications have been filed with the USPTO, and licenses have been issued to US companies on all intellectual property developed by our team. Eight papers have been published in refereed high impact journals. Multiple students at the undergraduate and graduate levels have been trained through their participation in this projects.
