(4cl) Exploring Interfacial Phenomena in Organic Photovoltaic Devices Using Block Copolymers

Polymer-based organic photovoltaic (OPV) cells have attracted much attention in recent years due to the promise of power sources that are flexible, lightweight, and inexpensive to fabricate. To date, the most efficient devices are bulk heterojunction cells composed of an active layer blend of an electron-donating polymer and an electron-accepting soluble fullerene derivative. By tuning the solution deposition conditions and post-processing treatments, power conversion efficiencies in these devices have reached values greater than 7%. Significantly, the performance of these cells is inherently linked to the structure at the electron donor-acceptor interface and at the electrode-active layer interfaces. However, these interfaces remain largely uncharacterized, which leads to a limited understanding of the structure-property relationships in these devices. Here we present a series of strategies for rationally controlling the: 1) intermolecular structure, 2) active layer phase separation, and 3) electrode surfaces in order to understand the correlation between these crucial materials junctions and device performance. Each of these approaches relies on the design of block copolymers with specific functionality. By tailoring the chemical structure of these macromolecules, we are able to systematically and rigorously characterize the self-assembled microstructures that are formed. And, finally, these materials are incorporated as functional components in photovoltaic devices. Importantly, because the resultant morphologies have inherently distinct domains, we are able to correlate interfacial structure with electronic performance in operational devices. These relationships, in turn, will provide a structured pathway for future plastic solar cell designs.