Electrochimica Acta 56 (2011) 9159–9161 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Dye-sensitized solar cell based on optically transparent TiO 2 nanocrystalline electrode prepared by atomized spray pyrolysis technique H.M.N. Bandara a,b,∗ , R.M.G. Rajapakse a , K. Murakami b , G.R.R.A. Kumara a , G. Anuradha Sepalage a a Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka b Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8011, Japan a r t i c l e i n f o Article history: Received 26 April 2011 Received in revised form 26 July 2011 Accepted 26 July 2011 Available online 5 August 2011 Keywords: Transparent TiO2 Thin-ﬁlm Solar cell a b s t r a c t Preparation of crack-free thin ﬁlms of interconnected and non-agglomerated TiO 2 nanoparticles on elec- tronically conducting ﬂuorine doped tin oxide surfaces is instrumental in designing and developing transparent dye-sensitized solar cells (DSCs). A novel technique called “Atomized Spray Pyrolysis” (ASP) has been designed and developed to achieve such perfectly transparent thin ﬁlms. Optical transmittance of TiO 2 ﬁlms produced on FTO surface by this ASP method has been compared with those obtained by doctor-blading and by hand spray methods and found that the atomized spray pyrolysis technique give ﬁlms with high transparency. Dye adsorption per gram of TiO 2 is 2.16 times higher in the sample produced by the ASP method when compared to the ﬁlm produced by the hand spray method and is 1.60 times higher than that produced by the doctor-blading method using a commercially available TiO 2 nanocrys- talline paste. SEM studies show the presence of interconnected discrete particles in the ﬁlm produced by the ASP method. The ﬁll factor (ff) remains almost constant for the cells with thickness from 6 m to 13 m but the highest photovoltage and photocurrent were found in ∼10 m ﬁlm based DSC which gave 8.2% conversion efﬁciency at AM 1.5 irradiation for cells of 0.25 cm 2 active area. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The dye-sensitized solar cell (DSC) reported by Gratzel and co-workers in 1991 [1] is a signiﬁcant innovation of solar cell tech- nology and the innumerable advancements made on this unique device has now resulted in 11.5% solar-to-electricity conversion efﬁciency [2]. The working mechanism and each and every process associated with it have been thoroughly studied over the last two decades and, as such, this innovation has immensely contributed also to the advancement of scientiﬁc knowledge of thermodynamic and kinetic aspects of electron injection, transport along intercon- nected semiconductor particles, trapping and detrapping and so on. The Gratzel cell utilizes interconnected particles of about 20 nm average diameter and packed in a layer of ∼15 m thickness[2]. The preparation of the TiO 2 layer is critical in optimizing the per- formance of the DSC. The commonly used methods involve the doctor-blading, hand-spraying or screen printing of a TiO 2 sol prepared by a sol–gel method. Best cell performances are usu- ally observed when screen printing or spray techniques are used. However, direct spray of aerosol particles of ethanolic TiO 2 on to conducting FTO substrates usually forms aggregates of particles ∗ Corresponding author at: Department of Chemistry, University of Peradeniya, Sri Lanka. Tel.: +94 81 2394441; fax: +94 81 2388018. E-mail address: hmnb@pdn.ac.lk (H.M.N. Bandara). thereby reducing the surface area available for dye adsorption and the pore volume for electrolyte penetration. Therefore, the devel- opment of a technique which could spray such nanoparticulate sols on to conducting glass substrates producing thin ﬁlms consisting of discrete particles and avoiding aggregates for utilization in the construction of DSCs is desirable. The nanocrystalline TiO 2 elec- trodes made from interconnected, non-aggregated nanoparticles are transparent, and hence they could be used to fabricate DSCs on window panes of houses to harness energy while allowing some light to pass through the windows. It is also possible to fabricate such transparent DSCs on transparent lamp shades to convert some of the light back to electricity. Therefore, the design, development, fabrication and testing of transparent DSCs are very important not only from the academic point of view but also in a commercial perspective. In connection with the preparation of transparent TiO 2 ﬁlms on conducting glass, Doherty and Fitzmaurice [3] have reported the preparation and characterization of those possessing well- deﬁned morphologies. They used Langmuir–Blodgett technique for depositing monolayers of TiO 2 sols prepared by the hydrolysis of titanium tetraisopropoxide in non-aqueous medium in the pres- ence of cetyltrimethylammonium bromide (CTAB) as a stabilizer and tetramethylammonium hydroxide (TMAH) as a catalyst in the presence of trace amounts of water. The ﬁlms deposited had uni- form distribution of (2.2 ± 0.2) nm spherical particles with optical absorption onset of 360 nm. The heat treatment has interconnected 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.07.119