Photoelectrochemical properties of Zn(II) phthalocyanine/ZnO nanocrystals heterojunctions: nanocrystal surface chemistry effect C. Ingrosso a , A. Petrella a , M.L. Curri b, * , M. Striccoli b , P. Cosma a,b , P.D. Cozzoli a , A. Agostiano a,b a Dipartimento di Chimica, Universita ` di Bari, via Orabona 4, I-70126 Bari, Italy b CNR IPCF Sez. Bari c/o Dip. di Chimica, Universita ` di Bari, Bari, Italy Available online 7 January 2005 Abstract Hetero-junctions prepared by deposition of unsubstituted Zn(II) phthalocyanines (Zn(II)Pc) onto a film of colloidal ZnO nanocrystals, were studied. Photoelectrochemical measurements were performed on the sensitized nanocrystalline ZnO films deposited onto optically transparent electrodes, to characterize the photoactivity of the heterojunction. A comparison between ZnO nanocrystals prepared by using a hydrolytic and non-hydrolytic route was performed in order to investigate the effect of nanocrystal surface chemistry on the photoelectrical response. The photoactivity was found to be significantly enhanced when non-hydrolytically prepared nanocrystals were used to form the heterojunction. # 2004 Elsevier B.V. All rights reserved. PACS: 73.40.-c; 73.50.-h; 73.61.Tm; 82.45.+z Keywords: Dye-sensitized film; Colloidal nanocrystals; ZnO; Zn(II) phthalocyanine; Photoactivity 1. Introduction In recent years, increasing interest has been devoted to dye sensitised-semiconductor heterojunctions [1]. These systems create a convenient framework for investigating interfacial electron-transfer processes and can be effectively applied in energy conversion and photo- catalysis [2]. For both applications, heterojunctions based on wide band gap oxide nanocrystalline films present a high surface-to-volume ratio, resulting in a large number of interfaces and consequently in a highly efficient charge transfer. Typically in semiconductor–molecular dye systems, photogenerated electrons are injected from the excited state of the dye into the conduction band or surface states of the semiconductor. One of the distinguishing features of the nanocrystalline oxide– dye system is the relatively low rate of the back electron transfer from the conduction band of the semiconductor www.elsevier.com/locate/apsusc Applied Surface Science 246 (2005) 367–371 * Corresponding author. Tel.: +39 080 5442 027; fax: +39 080 5442 129. E-mail address: m.curri@area.ba.cnr.it (M.L. Curri). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.11.041