IP: 84.54.57.240 On: Fri, 27 Sep 2019 06:43:26 Copyright: American Scientific Publishers Delivered by Ingenta ARTICLE Copyright © 2013 by American Scientific Publishers All rights reserved. Printed in the United States of America Energy and Environment Focus Vol. 2, pp. 270–276, 2013 (www.aspbs.com/efocus) Performance of Porous, Nanocolumnar ZnO Electrodes Obtained at Low Temperature by Plasma-Enhanced Chemical Vapor Deposition in Dye-Sensitized Solar Cells A. G. Vega-Poot 1, 2 , M. Macias-Montero 3 , A. Barranco 3 , A. Borras 3 , A. R. Gonzalez-Elipe 3 , G. Oskam 2 , and J. A. Anta 1, * 1 Área de Química Física, Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, 41013 Sevilla, Spain 2 Departamento de Física Aplicada, CINVESTAV-IPN, Mérida, Yucatán, 97310, México 3 Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Avda. Américo Vespucio 49, 41092 Sevilla, Spain ABSTRACT The photovoltaic performance of dye-sensitized solar cells consisting of mesoporous ZnO nanocolumnar films prepared at low temperatures by plasma enhanced chemical vapor deposition is studied. The results have been compared with those of randomly packed nanoparticulate electrodes prepared by doctor-blading a suspension of two mixed commercial nanopowders and subsequent high temperature annealing. The characterization of the devices consisted of dye loading and current–voltage curve measurements. The charge collection efficiency was probed by electrochemical impedance spectroscopy (EIS) under illumination, intensity modulated photovoltage spectroscopy (IMVS) and intensity modulated photocurrent spectroscopy (IMPS). It has been found that the nanoparticulate electrodes produce larger photocurrents as a consequence of better dye loading. However, the combined EIS/IMPS/IMVS study provides self-consistent evidence that transport properties are similar for both kinds of electrodes, approaching a 100% collection efficiency in both cases. The possibility of using ZnO nanostructures obtained by low-temperature processing methods for low-cost DSC is discussed. KEYWORDS: ZnO Nanowires, Dye-Sensitized Solar Cells, Electrochemical Impedance Spectroscopy, Electron Transport Properties. 1. INTRODUCTION ZnO is a well-known metal-oxide n-type semiconductor with interesting applications in photovoltaics, such as in dye-sensitized solar cells (DSC) 1 extremely thin absorber solar cells, 2 and hybrid solar cells. 3 ZnO is capable of yielding different electrode morphologies in a tailored way by using a large variety of preparation methods. 5 It has good electron transport properties in the bulk and an adequate band gap for applications in DSC. 5 ZnO- based photoanodes have reached a record efficiency of a 7.5% under 1-sun illumination by means of hierarchical nanostructures. 6 However, it has been pointed out 7 that efficiencies of ZnO-based DSC remain far from their TiO 2 counterparts and that new synthetic routes, rather than new morphologies, are more interesting to be investigated. ∗ Author to whom correspondence should be addressed. Email: anta@upo.es Received: 28 September 2013 Accepted: 14 October 2013 In this regard recombination and/or injection losses for nanostructures obtained from electrodeposition in aqueous solution 8 have been detected. Furthermore poor electron injection from the excited dye to the semiconductor 9 10 has also been claimed to explain the low performance of ZnO- based DSCs. Preparation procedures of ZnO photoanodes for DSC applications can be divided in wet and dry methods. The first types are by far the most used, including hydrothermal synthesis, 11 12 spray pyrolysis, 6 electrodeposition, 13 14 etc. All these techniques, including dry methods like chemi- cal vapor deposition 15 require high temperature processing steps to prepare the photoanodes. In this work we test the photovoltaic performance of 1-dimensional ZnO electrodes prepared by plasma- enhanced chemical vapor deposition (PECVD), 16 a one- step technique, which, to our knowledge, has not been previously utilized to prepare ZnO electrodes for DSCs. The application of this technique in the fabrication 270 Energy Environ. Focus 2013, Vol. 2, No. 4 2326-3040/2013/2/270/007 doi:10.1166/eef.2013.1062