Article pubs.acs.org/JPCC
Comprehensive Investigation of Silver Nanoparticle/Aluminum Electrodes for Copper Indium Sulfide/Polymer Hybrid Solar Cells Mario Arar,†,‡ Andreas Pein,§ Wernfried Haas,‡,∥ Ferdinand Hofer,∥ Kion Norrman,⊥ Frederik C. Krebs,⊥ Thomas Rath,†,‡ and Gregor Trimmel*,†,‡ †
Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria Christian Doppler Laboratory for Nanocomposite Solar Cells, Graz University of Technology and NanoTecCenter Weiz Forschungsgesellschaft mbH, Austria § Polymer Competence Center Leoben GmbH, Roseggerstrasse 12, 8700 Leoben, Austria ∥ Institute for Electron Microscopy and Fine Structure Research, Graz University of Technology and Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz, Austria ⊥ Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde, Denmark ‡
S Supporting Information *
ABSTRACT: Electrode materials are primarily chosen based on their work function to suit the energy levels of the absorber materials. In this paper, we focus on the modification of aluminum cathodes with a thin silver interlayer (2 nm) in copper indium sulfide/poly[(2,7-silafluorene)-alt-(4,7-di-2thienyl-2,1,3-benzothiadiazole)] (PSiF-DBT) nanocomposite solar cells, which improves the fill factor compared to pure aluminum electrodes. A comprehensive structural investigation was performed by means of transmission electron microscopy and time-of-flight secondary ion mass spectrometry revealing the presence of silver nanoparticles in an aluminum oxide matrix between the absorber layer and the aluminum cathode. In combination with complementary optical investigations, the origin of the improvement is ascribed to a facilitated charge extraction.
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copper indium sulfide18,19 and selenide,20,21 and lead sulfide22 and selenide.23 The hybrid solar cells investigated in this work comprise in situ prepared copper indium sulfide (CIS) nanoparticles embedded in a poly[(2,7-silafluorene)-alt-(4,7-di-2-thienyl2,1,3-benzothiadiazole)] (PSiF-DBT) matrix. The in situ preparation procedure offers the advantage that (i) no additional nanoparticles synthesis step using capping agents and their subsequent removal or exchange is necessary and (ii) an unobstructed polymer/nanoparticle interface facilitating charge separation is achieved.12 Following this procedure, metal xanthate precursors (copper and indium O-2,2dimethylpentan-3-yl dithiocarbonate) are mixed with the polymer, coated onto a substrate, and via a thermal conversion step the desired nanoparticles are formed inside the polymer matrix through decomposition of the precursors.18 Byproducts during decomposition are volatile and do not remain in the layer. The facile process and low temperature needed (
