(603h) Role of Oligomeric Additives on P3HT/PCBM Domain Interfaces and Photovoltaic Performance

Controlling the nanophase separation of donor-type polymers and fullerene-based acceptors in bulk heterojunction (BHJ) thin films is crucial to optimizing the performance and enhancing the stability of organic photovoltaics (OPV) devices. A variety of strategies, including thermal or solvent annealing or incorporating small molecule processing aids or block copolymer compatibilizers, have been used as a way to mediate phase segregation and enhance OPV performance. In this presentation, we describe our efforts to characterize the influence of oligomeric donor-type materials based on phase segregation and performance of BHJ thin films comprising poly(3-hexylthiophene) and PCBM fullerenes. A combination of electron microscopy and X-ray and neutron scattering methods, augmented with insights from multiscale modeling, are used to develop a picture of how the size of low molecular weight P3HT additives and their loading level influences the distribution of the additives and their molecular orientation at donor-acceptor interfaces. These features of nanoscale structure are correlated with results from device performance testing, providing useful insights into the links between additive design, BHJ structure and device performance. While results are specific to P3HT/PCBM systems, we believe that the findings are generally applicable to systems where miscibility, crystallization, and packing at interfaces conspire to affect structure and performance of OPV devices based on the BHJ concept.