Preparation of transparent and conducting boron-doped ZnO electrode for its application in dye-sensitized solar cells Bhagwat N. Pawar a , Gangeri Cai a , Dukho Ham a , Rajaram S. Mane a , T. Ganesh a , Anil Ghule, Ramphal Sharma a , K.D. Jadhava b , Sung-Hwan Han a,Ã a Department of Chemistry, Hanyang University, Sungdong-Ku, Haengdang-dong 17, Seoul 133-791, Republic of Korea b Bharati Vidyapeeth University,Y.M. College, Pune-411038, India. article info Article history: Received 12 September 2008 Received in revised form 5 December 2008 Accepted 5 December 2008 Available online 20 January 2009 Keywords: Boron-doped ZnO film electrode Spray pyrolysis Conductivity Dye-sensitized solar cells abstract A simple and economic chemical spray pyrolysis method is used to prepare transparent and conducting boron-doped zinc oxide (B n ZnO) electrode having potential applications in dye-sensitized solar cells (DSSCs). The B n ZnO electrodes were critically characterized for their structural, morphological and electrical properties. The B n ZnO electrode with 2 at% boron doping showed average grain size of 20(71) nm, surface roughness of 9 nm, X95% transparency and resistivity of 4.5  10 3 O cm 1 . Furthermore, doping concentration of boron could also be easily controlled for achieving desired properties. Using this electrode as a substrate in DSSCs, the solar-to-electrical conversion efficiency with N3 dye as a sensitizer was noted to be 1.53%. This work suggests that the B n ZnO electrodes could be used as promising alternative to presently used indium- or fluorine-doped tin oxide as substrates. & 2008 Elsevier B.V. All rights reserved. 1. Introduction Zinc oxide (ZnO) is considered the workhorse of the recent technological developments for its envisaged applications ranging from semiconductors (properties like chemical and thermal stability, wide band gap 3.37eV and exciton binding energy 60 mV), surface acoustic wave filters, photonic crystals, light- emitting diodes, photodetectors, optical modulator waveguides, phosphor material in cathode-ray tube screens, varistors, gas sensors, short-wavelength semiconductor diode lasers, solar cells, etc. [1–8]. Morphology, size and size distribution of ZnO nanoparticles play an important role in deciding the properties and thus different forms of ZnO have been synthesized via a variety of techniques with the intension of enhancing the solar-to- electrical energy conversion efficiency. Bulk ZnO is an insulator; however, when fabricated in the form of thin films it shows semiconductor properties. This transition from insulator to semiconductor occurs as a result of its deviation in stoichiometry. The properties of ZnO films depend on the preparative methods, growth conditions and its chemical composition. Doped ZnO thin films show relatively low resistivity, high transmittance and chemical stability when compared with undoped ZnO thin films [9]. These doped ZnO thin films could be used as an active electrode in dye-sensitized solar cells (DSSCs); however, they are yet to be explored. Although, there are several physical and chemical methods used for the preparation of thin films, a simple and economic method capable of incorporating foreign impurities (dopants), having high growth rate, mass production capability and forming uniform coating over a large surface area is generally desired. Among the available deposition techniques, chemical spray pyrolysis shows promising future and thus we have focused our attention to study the feasibility of this technique in synthesis of conducting and transparent boron-doped ZnO (B n ZnO) electro- des to be used in DSSCs. Obtaining transparent and conducting B n ZnO thin films is a great challenge, especially when higher transparency and minimum resistivity is desired for which boron doping concentration have to be tuned within 1–5 at%. This work is motivated from the fact that the applications of B n ZnO electrodes (prepared using spray pyrolysis) as an active electron collector in DSSCs is yet to be reported. Herein this letter, we have studied that by varying boron doping concentrations, the desired properties (conductivity, transparency, resistivity and roughness) can be tailored. The B n ZnO films were characterized for their structural, optical, electrical and morphological properties. We have also demon- strated the use of this B n ZnO electrode as an active electrode in ZnO-based dye-sensitized solar cells. 2. Experimental details About 0.5 M zinc acetate dihydrate [Zn(CH 3 COO) 2  2H 2 O] aqueous solution was prepared by dissolving Zn(CH 3 COO) 2  2H 2 O in a mixture of deionized water and methanol (volume ratio of ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2008.12.010 Ã Corresponding author. Tel.: +822 2292 5212; fax: +822 2299 0762. E-mail address: shhan@hanyang.ac.kr (S.-H. Han). Solar Energy Materials & Solar Cells 93 (2009) 524–527