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. Myriad strategies ranging from controlling thermal or solvent annealing profiles to incorporating small molecule processing aids or block copolymer compatibilizers, to name a few, have been used in this pursuit. In this presentation, we describe our efforts to characterize the influence of oligomeric donor-type materials on phase segregation and performance of BHJ thin films based on poly(3-hexylthiophene) and PCBM fullerenes. A combination of multiscale modeling, electron microscopy and X-ray and neutron scattering methods are brought to bear to show how molecular weight and loading levels influence the distribution of additives and their molecular orientation at donor-acceptor interfaces. These morphological changes will be correlated to power conversion efficiencies, 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.

Role of oligomeric additives on P3HT/PCBM domain interfaces and photovoltaic performance

251st National Meeting (2016)

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