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

Abstract

Abstract 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‐C 61 ‐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.