The role of energy level matching in organic solar cells-Hexaazatriphenylene hexacarbonitrile as transparent electron transport material

We introduce the material hexaazatriphenylene hexacarbonitrile (HATCN) as electron conducting window layer for separating the photoactive region from the cathode in organic p-i-n type solar cells. HATCN has a wide band gap of 3.3 eV and is thus transparent in the visible range of the solar spectrum. Its electrical properties can be tuned by means of molecular n-doping which leads to an increase of electron conductivity by several orders of magnitude up to 2.2 x 10(-4) S/cm. However, an application in photovoltaic devices is restrained by its exceptionally high electron affinity, estimated 4.8 eV, which introduces an electron injection barrier to the photoactive acceptor material C(60). Here, we present a strategy to remove this barrier by means of introducing doped and undoped C(60) intermediate layers, thus demonstrating the importance of energy level matching in a multiple layer structure and the advantages of Fermi level control by doping. (C) 2010 Elsevier B.V. All rights reserved.