Dye sensitization of nanocrystalline TiO 2 by perylene derivatives Shu Wang a , Yuliang Li a,* , Chimin Du a , Zhiqiang Shi a , Shengxiong Xiao a , Daoben Zhu a , Enqin Gao b , Shengmin Cai b a Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China b College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China Received 11 September 2001; received in revised form 19 September 2001; accepted 27 December 2001 Abstract New sensitizing dye–semiconductor system comprised of 3,4,9,10-perylene tetracarboxylic acid (PTCA) or perylene 3,4-dicarboxylic- 9,10-(n-butylamine) carboximide (PNDCA) on titanium dioxide (TiO 2 ) had been prepared and characterized. Good energy conversion efficiency was obtained. The film of PTCA on TiO 2 yielded an incident photo-to-current efficiency (IPCE) of approximately 40% in the wavelength region of 440 to 530 nm, while that for PNDCA was approximately 14% at the wavelength region from 460 to 510 nm. Further studies concentrated on the doping of this system with bromine (Br 2 ). The results indicated that the sensitizing wavelength region was red shifted, which was advantageous for solar light harvesting. Furthermore, the doped films gave lower quantum conversion efficiency than the non-doped films. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Dye sensitization; Nanocrystalline TiO 2 ; Perylene derivatives 1. Introduction Since Gra ¨tzel and co-workers [1] achieved an efficient light energy conversion using ruthenium bipyridyl com- plexes-sensitized high surface area TiO 2 nanocrystalline porous film, dye sensitization of TiO 2 nanocrystalline has attracted much attention on solar cell applications [2]. Most dye sensitization research continues to focus on derivatives of ruthenium bipyridyl dyes. However, since it is not alto- gether clear what the most critical factors are for the enhancement of the conversion efficiency of this class photovoltaic properties, the investigation and development of other sensitizing dyes are important to broaden our understanding of sensitizing materials in general. It has been generally agreed that the high-energy conversion effi- ciency can be attributed to the fast electron injection from the sensitizer to the semiconductor and much slower back electron transfer to the sensitizer [2a]. Most perylene deri- vatives possess this feature [3]. In addition, the high absor- bance in the visible (e  10 5 M 1 cm 1 ) range and emission from a singlet state with high quantum yield [4] are all the advantages for use as sensitizers. On the other hand, the hetero-supermolecules formed through covalent assembly of nanocrystalline TiO 2 with PTCA or PNDCA can be doped with Br 2 to yield composite system. The composite films can play a key role as promising new building blocks in super- molecular systems. Therefore, construction of new pery- lene–TiO 2 system constitutes to be a key research program due to its interesting potential application in solar cell. Based on above reasons, the perylene derivatives were chosen as sensitizers. Until now, reports on the sensitization of semi- conductor by dyes based on perylene derivatives are very few [5]. Here we report on the excellent absorption proper- ties and sensitization yields obtained from TiO 2 nanocrystal- line films sensitized by PTCA and PNDCA, and in further, the properties of the sensitized films doped by bromine. The structures of PTCA, PNDCA and the perylene–TiO 2 hetero- supermolecules are shown in Fig. 1. 2. Experimental section 2.1. Materials 3,4,9,10-Perylene tetracarboxylic dianhydride was com- mercially obtained from Aldrich. All the commercial sol- vents were re-distillated prior to use. The conductive glass (ITO, thickness 0.7 nm, 89:9  0:43% transmittance in visible range, 12:0  1:2 O/dm 2 ) was obtained from Wei- guang Conductive Film, China. The nanocrystalline TiO 2 Synthetic Metals 128 (2002) 299–304 * Corresponding author. Tel.: þ86-1062-588-934; fax: þ86-1062-588-934. E-mail address: ylli@infoc3.icas.ac.cn (Y. Li). 0379-6779/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0379-6779(02)00007-3