Seminar Abstract:
Reducing the cost of solar energy has been named one of the grand challenges for the 21st century by the National Academy of Engineering. Solution processed plastic solar cells are one path toward achieving this goal and have already demonstrated solar power conversion efficiencies as high at 10% in the lab and it is believed that more than 15% should be possible in tandem devices. While this level of performance is lower than has been achieved with conventional semiconductors, the ability to print from low cost inks onto plastic substrates at low temperatures and avoid the expenses associated with rare earth or monocrystalline semiconductors results in low costs per watt and rapid energy payback times. While the technology is still developing and thus the current modules are relatively low performance and expensive, the ability to fabricate semi-transparent and colored solar panels has enabled a range of niche applications inaccessible to inorganic solar cells.
While there has been remarkable success over the last several years at developing new materials and device structures to increase the efficiency of lab-scale organic solar cells, there is still a great deal that is not well understood about the underlying physics and materials science of these devices. After a brief introduction to the field, this talk will discuss our research in two areas of critical importance to the large scale commercialization of organic solar cells. The first topic will be the origin of non-langevin recombination kinetics in certain bulk heterojunction solar cell materials. Non-langevin recombination is an important enabling property for the low cost manufacturing of polymer solar cells. The second topic will discuss the use of ultrafast spectroscopy to identify the minimum driving force for electron transfer in polymer/fullerene blends, which is one of the primary factors determining the upper limit of efficiency for single junction organic solar cells. Our progress in both these areas has resulted from cross-disciplinary collaboration between researchers in academia, industry, and the national labs to better understand the underlying science and the ultimate potential of this emerging photovoltaic technology.