title: Analysis and modification of defective surface aggregates on PCDTBT:PCBM solar cell blends using combined Kelvin probe, conductive and bimodal atomic force microscopy.
abstract: Organic photovoltaic systems comprising donor polymers and acceptor fullerene derivatives are attractive for inexpensive energy harvesting. Extensive research on polymer solar cells has provided insight into the factors governing device-level efficiency and stability. However, the detailed investigation of nanoscale structures is still challenging. Here we demonstrate the analysis and modification of unidentified surface aggregates. The aggregates are characterized electrically by Kelvin probe force microscopy and conductive atomic force microscopy (C-AFM), whereby the correlation between local electrical potential and current confirms a defective charge transport. Bimodal AFM modification confirms that the aggregates exist on top of the solar cell structure, and is used to remove them and to reveal the underlying active layer. The systematic analysis of the surface aggregates suggests that the structure consists of PCBM molecules.
authors.affiliation: Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, United States of America.
authors.forename: Hanaul
authors.initials: H
authors.lastname: Noh
authors.affiliation: Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, United States of America.
authors.forename: Alfredo J
authors.initials: AJ
authors.lastname: Diaz
authors.affiliation: Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, United States of America.
authors.forename: Santiago D
authors.initials: SD
authors.lastname: Solares
keywords: Kelvin probe force microscopy; conductive atomic force microscopy; multifrequency AFM; organic photovoltaics; polymer solar cells; surface defects