N N N M Copyright © 2006 Society of Porphyrins & Phthalocyanines Corrole-sensitized TiO 2 solar cells Don Walker a , Shlomit Chappel b , Atif Mahammed c∏ , Bruce S. Brunschwig* a , Jay R. Winkler a , Harry B. Gray a , Arie Zaban* b and Zeev Gross* c∏ a Beckman Institute, California Institute of Technology, Pasadena 91125, USA b Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel c Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel Received 24 July 2006 Accepted 18 September 2006 ABSTRACT: We are investigating the properties of corrole-sensitized TiO 2 solar cells. The TiO 2 -ad- sorbed free base and Ga III corroles display cell efficiencies under AM 1.5 illumination that are about half that of a standard N3-sensitized cell (N3 = cis-bis(4,4ʼ-dicarboxy-2,2ʼ-bipyridine)dithiocyanato ruthenium(II)), while that of the Sn IV -based cell is much lower. The properties of the corrole-TiO 2 solar cells, along with results obtained with electrodes of lower conduction band energies clearly reveal that the reducing power of the singlet excited states of the free base and Ga III corrole, but not of the Sn IV derivative, is sufficiently high for efficient injection into the TiO 2 conduction band. Copyright © 2006 Society of Porphyrins & Phthalocyanines. KEYWORDS: corroles, sensitizers, solar cells. INTRODUCTION Dye-sensitized solar cells (DSSCs) show great promise as devices that can efficiently convert solar energy to electricity [1]. Of the many dyes that have been investigated as sensitizers, the most popular are derivatives of Ru II bipyridines and porphyri- noids (porphyrins, phthalocyanines, chloro- and bac- teriophylls, extended porphyrins) [2, 3]. The latter are attractive because their photophysical properties can be readily tuned by selective substitutions on their molecular frameworks and/or via variation of the central metal ion. Recent advances in the synthetic availability of triarylcorroles and the subsequent elucidation of their photophysical properties suggest that they might be particularly good sensitizers in DSSCs [4, 5] since their frontier orbitals are at higher energy than those of analogous porphyrins [4f]. We chose 5,10,15-(pentafluorophenyl)corrole [H 3 (tpfc)] and its metal complexes for initial study, as these exceptionally robust derivatives [4c,f, 5a] exhibit strong absorptions over a wide range of the visible spectrum. Also of importance is our finding that H 3 (tpfc) and its closed-shell metal derivatives are intensely fluorescent, a feature that becomes less prominent in complexes in which the central-atom spin-orbit coupling is very large [6]. In addition, selective sulfonation of the framework H 3 (tpfc) carbon atoms provides ready access to derivatives with substituents that are known to bind to metal oxide surfaces [7]. The structures of a number of porphyrinoid dyes and the most commonly used ruthenium dye are shown in Chart 1, along with corroles that possess two sulfonic acid groups directly attached to the corrole skeleton. The choice of two anchoring groups was made, based on investigations of the binding interactions of Ru II dyes that perform well as sensitizers in DSSCs [8, 9]. RESULTS AND DISCUSSION Nanoporous TiO 2 electrodes were immersed *Correspondence to: Bruce S. Brunschwig, email: bsb@its. caltech.edu, Arie Zaban, email: zabana@mail.biu.ac.il, Zeev Gross, email: chr10zg@tx.technion.ac.il ∏ SPP full member in good standing Journal of Porphyrins and Phthalocyanines Published at http://www.u-bourgogne.fr/jpp/ J. Porphyrins Phthalocyanines 2006; 10: 1259-1262 Published on web 11/16/2006