Research: Next-Generation Photovoltaic Technologies

Rethinking the idealized morphology in high-performance organic photovoltaics

Traditionally, organic photovoltaic (OPV) active layers are viewed as an interpenetrating network of pure polymers and fullerenes with discrete interfaces. Argonne researchers, working with collaborators at the University of Chicago, LBNL, and NIST, have shown that the OPV active layer of high-performance PTB7:fullerene OPV devices, in fact, involves hierarchical nanomorphologies ranging from several nanometers of crystallites to tens of nanometers of nanocrystallite aggregates in intermixed PTB7-rich and fullerene-rich domains, themselves hundreds of nanometers in size. These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer—and likely most polymer:fullerene systems—in OPV devices. This new understanding will lead to a rethinking of the idealized morphology in OPVs, and, ultimately, to pathways for further performance optimization.

Correlating efficiency and morphology in polymer:fullerene solar cells: Hierarchical nanomorphologies promote exciton dissociation and diagrammatic hypothesis of the refined BHJ model for polymer:fullerene devices.

References

• Nano Letters 11 (2011) 3707
• J. Am. Chem. Soc. 133 (2011) 3284

September 2011