The characteristics of chemical and heat stability properties of chromium–vanadium–aluminum co-doped zinc oxide films for dye-sensitized solar cells Y.C. Lin a, ⁎, C.H. Chang a , C.H. Shen a , P.W. Wang b , Y.C. Lee b a Department of Mechatronics Engineering, National Changhua University of Education, Changhua 50007, Taiwan b C SUN MFG. Ltd, No.17, 10 Road, Taichung Industrial Park, Taichung 40755, Taiwan abstract article info Article history: Received 2 October 2009 Received in revised form 12 May 2010 Accepted 28 May 2010 Available online 4 June 2010 Keywords: AZO:Cr:V Doped zinc oxide Chemical stability Heat stability Dye-sensitized solar cells Front contact Transparent conducting oxide thin films are used as front contact material for dye-sensitized solar cells. This study investigated the effects of chromium (Cr) and vanadium (V) contents on the chemical and heat stability properties of aluminum-doped zinc oxide (AZO) thin films using pulsed direct current magnetic sputtering on Corning 1737F glass substrates. The experimental results show that Cr and V doping is useful for improving the chemical and thermal stability of AZO films. The energy gap for AZO thin films is between 3.65 and 3.69 eV. The resistivity of the AZO:Cr:V thin film was 4.23 × 10 –4 Ω cm at a Cr/V ratio of 0.30/0.23 wt. %, deposition power of 150 W, working distance of 5.5 cm, substrate temperature of 473 K, working pressure of 0.4 Pa, and frequency of 10 kHz. This value is lesser than (and therefore superior to) the resistivity of SnO 2 : F (FTO) films (6.5 × 10 –4 Ω cm), but greater than that of SnO 2 :In (ITO) thin films (1.2 × 10 –4 Ω cm). The resistivity increased by about 0.27% after electrolyte etching, which is similar to the 0.16% increase observed for the ITO thin film. After a thermal cycle test at 673 K, the resistivity of the AZO:Cr:V film increased to 5.42 × 10 –4 Ω cm, which is better than the resistivity of the ITO and FTO films after the same thermal cycle. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Because transparent conducting oxides (TCOs) possess favorable resistivity and high transmittance properties, they can be widely applied to flat panel displays, solar cells, and light-emitting diodes [1–4]. Currently, non-metal TCOs are divided into two categories: SnO 2 -based and ZnO-based TCOs [5]. The optoelectronic properties of AZO thin films [6] are highly similar to those of ITO thin films [7] due to improvement in the process parameters. In addition, the production cost and toxicity of AZO thin films are less than those of ITO thin films. AZO thin films also have better stability during the hydrogen plasma process [8]. At present, the price of zinc is lower, and the use of zinc can reduce the reliance on indium. However, the chemical and heat stability of AZO thin films [9,10] are compara- tively inferior. A dye-sensitized solar cell (DSSC) is one type of potential organic solar cell [11]. If ITO thin films are used as the front contact material, the resistivity increases dramatically during the processes of electro- lyte corrosion and high temperature sintering at 723 K over a period of 1 h, thus causing the DSSC efficiency to decline [12]. Because Cr has excellent corrosion resistance and heat stability properties and V also has good corrosion resistance to acid and alkaline solutions, doping a small amount of Cr and V into AZO may increase chemical stability [13] and temperature endurance. Previous studies related to DSSC front contacts [10,12], FTO, and SnO 2 :Sb (ATO) [14,15] have attempted to replace ITO with a more suitable alternative material; however, to date, the use of ZnO-based TCOs as a DSSC front contact has not been studied. 2. Experiment This study investigates the effect of Cr and V contents on the chemical and heat stability properties of AZO thin films using pulsed DC magnetic sputtering on Corning 1737F glass substrates. First, a pure aluminum metal piece (purity 99.9%, size: φ = 3 mm, thickness: 1.5 mm) was adjusted to determine the optimum aluminum (Al) doping concentration for an AZO target with the lowest resistivity. Second, pieces of Cr and V metals (purity 99.9%, size: φ = 2 mm round, thickness: 1.5 mm) were placed at different positions on the AZO thin film, and the different doping content of Cr (0.17 ∼ 0.59 wt.%) and V (0.13 ∼ 0.45 wt.%) thin films were prepared with power 150 W, work pressure 0.4 Pa with argon as a background gas, pulsed frequency 10 kHz, film thickness 250 nm, substrate temperature 473 K and without bias during deposited process. After the deposition, the AZO: Cr:V thin film resistivity and optical transmittance in the visible region was observed. Then, to investigate the corrosion resistance of Thin Solid Films 518 (2010) 6055–6060 ⁎ Corresponding author. Tel.: + 886 4 7126207; fax: + 886 4 7211149. E-mail address: ielinyc@cc.ncue.edu.tw (Y.C. Lin). 0040-6090/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2010.05.122 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf