title: Elemental mapping of interfacial layers at the cathode of organic solar cells.
abstract: One of the limitations in understanding the performance of organic solar cells has been the unclear picture of morphology and interfacial layers developed at the active layer/cathode interface. Here, by utilizing the shadow-Focused Ion Beam technique to enable energy-filtered transmission electron microscopy imaging in conjunction with X-ray photoelectron spectroscopy (XPS) experiments, we examine the cross-section of polythiophene/fullerene solar cells to characterize interfacial layers near the semiconductor-cathode interface. Elemental mapping reveals that localization of fullerene to the anode interface leads to low fill factors and S-shaped current-voltage characteristics. Furthermore, the combination of elemental mapping and XPS depth profiles of devices demonstrate oxidation of the aluminum cathode at the active layer interface for devices without S-shaped characteristics and fill factors of 0.6. The presence of a thin dielectric at the semiconductor-cathode interface could minimize electronic barriers for charge extraction by preventing interfacial charge reorganization and band-bending.
authors.affiliation: Department of Chemical Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Gopal K
authors.initials: GK
authors.lastname: Mor
authors.forename: Thinh P
authors.initials: TP
authors.lastname: Le
authors.forename: Kiarash
authors.initials: K
authors.lastname: Vakhshouri
authors.forename: Derek R
authors.initials: DR
authors.lastname: Kozub
authors.forename: Enrique D
authors.initials: ED
authors.lastname: Gomez
keywords: FIB; P3HT; PCBM; contacts; energy-filtered TEM; organic photovoltaics