title: A real-time study of the benefits of co-solvents in polymer solar cell processing.
abstract: The photoactive layer of organic solar cells consists of a nanoscale blend of electron-donating and electron-accepting organic semiconductors. Controlling the degree of phase separation between these components is crucial to reach efficient solar cells. In solution-processed polymer-fullerene solar cells, small amounts of co-solvents are commonly used to avoid the formation of undesired large fullerene domains that reduce performance. There is an ongoing discussion about the origin of this effect. To clarify the role of co-solvents, we combine three optical measurements to investigate layer thickness, phase separation and polymer aggregation in real time during solvent evaporation under realistic processing conditions. Without co-solvent, large fullerene-rich domains form via liquid-liquid phase separation at ~20 vol% solid content. Under such supersaturated conditions, co-solvents induce polymer aggregation below 20 vol% solids and prevent the formation of large domains. This rationalizes the formation of intimately mixed films that give high-efficient solar cells for the materials studied.
authors: 1] Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands [2] Dutch Polymer Institute P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
authors: Jacobus J
authors: JJ
authors: van Franeker
authors: BASF Schweiz AG, Schwarzwaldallee 215, CH-4002 Basel, Switzerland.
authors: Mathieu
authors: M
authors: Turbiez
authors: 1] Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands [2] Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P.R. China.
authors: Weiwei
authors: W
authors: Li
authors: 1] Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands [2] Dutch Polymer Institute P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
authors: Martijn M
authors: MM
authors: Wienk
authors: 1] Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands [2] Dutch Polymer Institute P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
authors: René A J
authors: RA
authors: Janssen