MIP-type organic solar cells incorporating phthalocyanine/fullerene mixed layers and doped wide-gap transport layers J. Drechsel a, * ,B.M€ annig a , D. Gebeyehu a , M. Pfeiffer a ,K.Leo a ,H.Hoppe b a Institut f € ur Angewandte Photophysik, Technische Universit€ at Dresden, D-01062 Dresden, Germany b Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, University Linz, A-4040, Linz, Austria Received 21 August 2003; accepted 18 November 2003 Available online 13 December 2003 Abstract We describe a simple organic solar cell structure that allows to study in detail loss mechanisms due to non-ohmic contacts, structural drawbacks and material selection: the MIP-type (metal-intrinsic-p-doped) structure discussed here represents the p-side and the active layer within a PIN type solar cell architecture. We here adapt the bulk hetero- junctionconceptusingblendsofzinc-phthalocyanine(ZnPc)andbuckminsterfullereneC 60 .Furthermore,weusedoped wide-gap materials as hole transport layers that enable a more sophisticated solar cell development. The samples are characterized by combination of current voltage characteristics, impedance spectroscopy and capacitance–voltage measurements.WepresentanevolutionofMIP-typestructureswhichimprovesallsolarcellparameters;inparticular, excessive series resistance and contact problems reducing the fill factor could be almost completely eliminated. Ó 2003 Elsevier B.V. All rights reserved. PACS: 72.80.Le; 73.50.Pz; 72.40.+w Keywords: Organic solar cell;Wide-gaptransportlayers;Capacitance–voltage;Impedancespectroscopy;Donor–acceptorblend;Zinc- phthalocyanine; C 60 1. Introduction Organic semiconducting materials are currently regarded as a promising alternative in the field of photovoltaics, particularly for large-area solar cells [1]. The main advantages are the flexibility and the potentially low cost production involving exclusively low temperature processes. The con- tinuous efficiency improvements that have been achievedrecently[2–5]areencouragingfromboth research and applications perspectives. Our basic approach to organic solar cells is based on small molecule physical vapor deposited multilayer structures. Many single or multilayer structures have been proposed so far by several groups [2,4,6–8]. Depending on materials and layer sequences, power efficiencies of up to 3.6% have been achieved [4,5]. A major problem, how- ever,istheratherpoortransportcapabilitiesofthe typicallyundopedmaterials.Gaseousdopingwith * Corresponding author. Tel.: +49-35146335117; fax: +49- 35146337065. E-mail addresses: drechsel@iapp.de (J. Drechsel), pfeiffer@ iapp.de (M. Pfeiffer). URL: http://www.iapp.de. 1566-1199/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2003.11.005 Organic Electronics 5 (2004) 175–186 www.elsevier.com/locate/orgel