New diruthenium acetylide donor complexes for bulk-heterojunction solar cells

Conjugated polymers and oligomers have received a lot of attention as active materials for organic photovoltaic devices because of their potential for the development of plastic solar cells that are lightweight, flexible, and low cost. Bulk heterojunctions fabricated by blending polymers with fullerene derivative have resulted in great improvements in the polymer photovoltaic cell efficiencies. The most commonly used materials are poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) [1], these cells with optimized device structure and fabbrication conditions can reach efficiencies in the range of 5-5.5%. However, to produce highly efficient organic photovoltaic devices, it is necessary to extend the light absorption into the near-infrared region and at the same time preserve the high IPCE and open-circuit voltage. Several papers have been recently dedicated to the investigation of the use of conjugated polymers incorporating heavy atoms; in particular Pt acetylide polymers as donors in solar cells using PCBM as acceptor [2] were proposed as a tool to enhance charge photogeneration. For instance, Mei et al. reported on a Pt acetylide-based polymer using a 2,1,3-benzothiadiazole (BTD) acceptor moiety flanked on either side by 2,5-thienyl (Th) donor units ([-Pt(L2)-t-Th-BTD-Th-t-]n, where L = PBu3), which absorbs strongly throughout the visible region. [3] The use of Ru acetylides is a novel interesting tool for the design of donor materials [4] to combine with electron-withdrawing fullerides in bulk heterojunction solar cells. New dinuclear Ru(II) complexes where two Ru atoms are separated by a bridge consisting of a 2,1,3 benzothiadiazole acceptor moiety flanked on either side by 2,5-thienyl or 3-hexyl substituted 2, 5 thienyl donor units were synthesized. (Figure 1) These rather simple complexes appears to behave as a photoactive donor when blended with a fullerene as acceptor, thus being a first step toward novel bulk heterojunction solar cells, based on Ru donor systems Figure 1 1. F. Padinger, R. S. Rittberger, N. S Sariciftci, Adv. Funct. Mater, 13 (2003) 85–88. 2. W.-Y. Wong, C.-L. Ho, Acc. Chem. Res. 43 (2010) 1246. 3. J.Mei, et al. Appl. Mater. Interfaces 1 (2009) 150. 4. A. Colombo, C. Dragonetti, D. Roberto, R. Ugo, L. Falciola, S. Luzzati, and D. Kotowski Organometallics (2011) doi: 10.1021om100846e