Stable Inverted Polymer/Fullerene Solar Cells Using a Cationic Polythiophene Modified PEDOT:PSS Cathodic Interface

• Published in: Advanced functional materials 2010-08, Vol.20 (15), p.2404-2415
• Main Authors: Rider, David A., Worfolk, Brian J., Harris, Kenneth D., Lalany, Abeed, Shahbazi, Kevin, Fleischauer, Michael D., Brett, Michael J., Buriak, Jillian M.
• Format: Article
• Language: English
• Subjects: electrochemical deposition; fullerene; layer-by-layer assembly; organic photovoltaics; polythiophene
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201000304

A cationic and water‐soluble polythiophene [poly[3‐(6‐pyridiniumylhexyl)thiophene bromide] (P3PHT+Br−)] is synthesized and used in combination with anionic poly(3,4‐ethylenedioxythiophene):poly(p‐styrenesulfonate) (PEDOT:PSS)− to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer‐by‐layer assembly with colloidal suspensions of (PEDOT:PSS)−, and ii) modification of an electrochemically prepared (PEDOT:PSS)− film on ITO. The coatings are found to modify the work function of ITO such that it could act as a cathode in inverted 2,5‐diyl‐poly(3‐hexylthiophene) (P3HT)/[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer‐by‐layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency ∼2%) with significant long‐term stability in excess of 500 h. The electrostatic layer‐by‐layer assembly of a cationic polythiophene with either colloidal suspensions of anionic (PEDOT:PSS)– or electrochemically prepared (PEDOT:PSS)– films on ITO is established. The hybrid films act as interfacial modifiers for ITO and enable efficient, long‐lived inverted polymer/fullerene photovoltaics.