Thin ZnO nanocrystalline films for efficient quasi-solid state electrolyte quantum dot sensitized solar cells Dimitrios Karageorgopoulos a, b , Elias Stathatos a, * , Evangelos Vitoratos b a Department of Electrical Engineering, Technological-Educational Institute of Patras, GR-263 34 Patras, Greece b Department of Physics, University of Patras, GR-26500 Patras, Greece highlights graphical abstract < Novel and facile method for thin ZnO nanocomposite films. < Different ZnO film morphologies with solution components variation. < CdSe quantum dots were assembled onto ZnO films via wet method. < 4.5% maximum photo- electrochemical cell performance of CdSe sensitized ZnO films. article info Article history: Received 8 June 2012 Received in revised form 2 July 2012 Accepted 13 July 2012 Available online 20 July 2012 Keywords: ZnO Thin films Quantum dot sensitized solar cells Quasi-solid state electrolyte abstract Thin transparent ZnO nanocrystalline films are prepared through a novel facile method based on an amino double edged polypropylene oligomer and zinc precursor. While amines were reacted with acetate groups of zinc acetate starting material, the polypropylene oligomers acted as template for the oxide formation. Different structural properties of the ZnO films were achieved varying the quantity of the oligomer in the starting solution. Spherical aggregated or monodispersed particles were formed with average sizes ranging from 10 to 30 nm. The films were employed in the construction of quantum dot sensitized solar cells using both CdS and CdSe. For first time a quasi solid state electrolyte was applied succeeding a maximum overall efficiency of 4.5% in the case of aggregated particles which could probably act as scattering centers. The quasi solid state electrolyte was a hybrid organiceinorganic material with SiO 2 edged groups while no water was used in any step of preparation of the host electrolyte for a pol- ysulfide redox couple. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Utilization of renewable energies is of major importance because of the increase in fossil energy costs and future shortages. Taking into account the present status in photovoltaic technology some progress has to be made in cost/Watt and applicability. For this reason developments on potentially cheaper solar cells have made based on mesoporous wide band gap metal oxides inorganic semiconductors [1e3]. Dye sensitized solar cells (DSSCs) for almost twenty years have proved themselves as low cost alternatives in conventional technology based on silicon [4,5]. The almost 12% efficiency of these cells is mainly due to the unique properties of the nanostructured metal oxides n-type semiconductors typically TiO 2 [6]. ZnO is also a wide band gap semiconductor with energy band structure and physical properties similar with TiO 2 [7]. However, it has higher electronic mobility (155 cm 2 v 1 s 1 vs to 10 5 cm 2 v 1 s 1 of TiO 2 ) favorable for electron transport, it is easily crystallized and aniso- tropically grow in a variety of morphologies [8,9]. One of the main factors that limit the efficiency of the DSSCs and increase their cost is the dye used for inorganic semiconductors sensitization in the visible and near IR region of the solar spectrum [10]. Ruthenium-based dyes are usually costly while their extinction * Corresponding author. Tel.: þ30 2610 369242; fax: þ30 2610 369193. E-mail address: estathatos@teipat.gr (E. Stathatos). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2012.07.034 Journal of Power Sources 219 (2012) 9e15