Hindawi Publishing Corporation International Journal of Photoenergy Volume 2013, Article ID 765297, 8 pages http://dx.doi.org/10.1155/2013/765297 Research Article Physical Properties of Macroporous Tungsten Oxide Thin Films and Their Impact on the Photocurrent Density I. Riech, 1 M. Acosta, 1 M. A. Zambrano-Arjona, 1 F. Peñuñuri, 1 M. Rosado-Mendoza, 1 E. Marín, 2 P. Rodríguez-Fragoso, 3 and J. G. Mendoza-Álvarez 3 1 Laboratorio de Ciencia de Materiales, Facultad de Ingenier´ ıa, Universidad Aut´ onoma de Yucat´ an, 97130 M´ erida, YUC, Mexico 2 Instituto Polit´ ecnico Nacional, Centro de Investigaci´ on en Ciencia Aplicada y Tecnolog´ ıa Avanzada, Unidad Legar´ ıa, Legaria 694, Colonia Irrigaci´ on, 11500 M´ exico, DF, Mexico 3 Departamento de F´ ısica, CINVESTAV-IPN, A.P. 14-740, 07000 M´ exico, DF, Mexico Correspondence should be addressed to I. Riech; ines.riech@uady.mx Received 9 July 2013; Accepted 1 September 2013 Academic Editor: David Lee Phillips Copyright © 2013 I. Riech et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tungsten trioxide (WO 3 ) flms were prepared using polystyrene spheres of two diferent diameters as a template in order to create porous layers. X-ray difraction data and electron microscopy images show that annealed flms exhibit polycrystalline structure with monoclinic phase and pore size of approximately hundred nanometers. Te optical band gap energies have been determined by photoacoustic spectroscopy as 3.17 eV, and this value was not afected by sample morphology. Low temperature photoluminescence spectra exhibit broad band in the blue region. Deconvolutions of PL spectra show that there are two transitions which intensity depends on thin flm pore size. We discuss the possible origin of this emissions associated with oxygen vacancies and surface states. A comparative study of the WO 3 flms used as photoanodes is presented and correlated with PL results. 1. Introduction Among transition metal oxides, tungsten trioxide (WO 3 ) has been extensively investigated due to its structural and physical properties. Te experimental evidence of advantages of using porous flms in a great variety of devices has been reported by several authors [1–3]. Such flms are suitable for those applications where large efective surface area is needed to enhance the contact between an electrode and electrolyte, as in the case of photoelectrochemical cells, or between thin flm and absorbed gas, as in the case of gas sensors. Taking into account the pore size, materials are classifed as microp- orous, mesoporous, and macroporous. Most of the reported papers are about the study of WO3 thin flms with porous size smaller than 50 nm (micro- and mesoporous). Less attention have been paid to macroporous tungsten oxide flms, despite they have a wider range of potential applications as an ion hosting material in electrochromic devices [4–6], chemical sensing [7], or photocatalysts [8]. According to the literature reports, the syntheses of the material and its morphological and structural properties have been investigated in much greater detail than electronic properties. However, in many applications, such as photocatalytic, it is important to control recombination centers which limit the efciency by the quick recombination of photogenerated carriers through it. To prepare WO 3 thin flms, several preparation tech- niques have been used: sol-gel [9], chemical vapor deposition [10], and radio frequency (RF) sputtering [11], among others. Te sol-gel technique has advantages over other deposition techniques because it provides low temperature growth and low cost. One of the methods to obtain porous thin flms by sol-gel technique is based on templating strategy which implies sol-gel synthesis, either within the porous of a membrane or around polystyrene spheres [4]. In the present study, we have obtained macroporous tungsten oxide flms by sol-gel with two diferent porous sizes using polystyrene microspheres (PS) as a template. We investigated the relationship between morphological and physical properties of these porous layers, and we compared them, for reference, with those of a compact layer grown