Exciton Dynamics and Charge Carrier Generation in Organic Semiconductors

The ever-increasing demand for cleaner sources of energy calls for inexpensive and highly efficient solar cells. Solution- and vacuum-processable organic solar cells have gained significant attention as an attractive source of energy owing to their continuously rising power conversion efficiency, low cost, thin device structure, and mechanical flexibility.
The absorption of light in organic solar cells generates a strongly bound electron-hole pair called an exciton. To efficiently dissociate the exciton into charges, a heterojunction composed of electron donating and accepting materials with suitable energy levels is typically used to provide the driving force needed to overcome the Coulomb attraction between the electron-hole pair. The photon-to-charge conversion in organic solar cells is a complex process that is subject to losses; hence, it is critical to carefully monitor every step from photon-to-charge conversion, such as exciton photogeneration, exciton diffusion towards the donor-acceptor interface, and exciton dissociation into charges. This thesis sheds light on the photon-to-charge conversion process in organic photovoltaics using a multi-disciplinary approach that combines results from steady-state and time-resolved spectroscopy, and Monte Carlo simulations.