Excited state dynamics of organic photovoltaics probed using ultrafast spectroscopy

2015-08-04Compared to inorganic silicon semiconductors, organic semiconductors possess many desirable properties such as flexibility, light weight and high absorption coefficient. These properties lead to low manufacturing and transportation costs for organic solar cells. However, the maximum efficiency obtained for organic solar cell is ~11% compared to 27% device efficiency for silicon semiconductor. This low device efficiency can be addressed with proper understanding of the working principles of organic solar cells. The active layer of an organic solar cell is composed of an electron donor and an electron acceptor material. Upon light absorption in the active layer, a series of processes: exciton generation, exciton diffusion, charge generation and charge recombination occur before the charges are collected at the electrode. The efficiency of the device depend on the efficiency of each of these processes. In this dissertation ultrafast spectroscopic techniques are utilized to provide insight into the dynamics and efficiency of these processes, which will eventually assist in optimizing the device performance for organic semiconductors