Applied Surface Science 274 (2013) 306–313 Contents lists available at SciVerse ScienceDirect Applied Surface Science jou rn al h omepa g e: www.elsevier.com/locate/apsusc On the properties of aluminium doped zinc oxide thin films deposited on plastic substrates from ceramic targets M. Girtan a,∗ , A. Vlad b,g , R. Mallet c , M.A. Bodea b , J.D. Pedarnig b , A. Stanculescu d , D. Mardare e , L. Leontie e , S. Antohe f a Angers University, Photonics Laboratory, LUNAM, France b Institute of Applied Physics, Johannes Kepler University, A-4040 Linz, Austria c Angers University, SCIAM, France d National Institute of Materials Physics, Bucharest, Romania e Faculty of Physics, Al.I. Cuza University, Iasi, Romania f Faculty of Physics, Bucharest University, Romania g National Institute for Lasers, Plasma and Radiation Physics, Bucharest, Romania a r t i c l e i n f o Article history: Received 7 September 2012 Received in revised form 15 February 2013 Accepted 9 March 2013 Available online 16 March 2013 Keywords: Plastic solar cells Plastics optoelectronics a b s t r a c t We report on the deposition of Al doped ZnO (AZO) thin films on unheated polyethylene terephthalate (PET) substrates by pulsed laser deposition technique using a UV excimer laser and Al 2 O 3 :ZnO ceramic targets (1.5 and 2 wt% Al 2 O 3 ). The deposited AZO films have been investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, and optical spectrophotometry. Films present excellent optical and electrical properties (transmission in the visible range T > 85%; resistivity at room temperature  = 1.3 × 10 -3  cm) as electrodes for plastic solar cells. A good correlation was found between deposition conditions (laser fluence) and structural, morphological, optical and electrical properties. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The new advancements in organic solar cells performance with a certified conversion efficiency of 9.2% achieved in 2012 [1], compa- rable to commercial amorphous silicon solar cells (8–11%), confirm that plastic solar cells will become one of the future solutions in energy conversion. Besides the increase of efficiency [2–6], other problems to solve are the improvement of devices stability [7–10] and the reduction of fabrication cost. Indium tin oxide (ITO) thin films deposited on rigid glass substrates have been extensively studied [11–15] and are widely used as transparent conducting electrodes in many optoelectronic devices [16–20]. However, the price and the limited resources of indium and the fragility of films deposited on glass indicate that is necessary to look for alternative solutions. Another transparent conducting oxide (TCO) is doped zinc oxide (ZnO). The main advantages of ZnO are that it is a non- toxic, inexpensive, and abundant semiconducting material with wide band gap energy E g = 3.3 eV. During the past years there have been many reports on doping of ZnO with different elements such as Ga, In, Al, F, N, Mg, and Cr [21–26] using various techniques ∗ Corresponding author at: Photonics Laboratory, Angers University, 2, Bd. Lavoisier, 49045 Angers, France. Tel.: +33 0241735359; fax: +33 0241735216. E-mail address: mihaela.girtan@univ-angers.fr (M. Girtan). for deposition such as sputtering [27–29], spin coating [30–33], thermal oxidation [34–36], chemical vapor deposition, spray [37–41], and pulsed laser deposition (PLD) [42–58]. Most of these studies are focused on films deposited on fragile substrates such as glass that cannot be deformed easily. For novel technical appli- cations, e.g. in plastic solar cells and plastic electronic devices, the deposition of films on flexible and light-weight substrate materials is required. The TCO thin films are usually deposited at high substrate temperature (400–550 ◦ C) which is not compatible with plastic substrates. The growth of good quality TCO films at room temper- ature is difficult and may require adequate deposition techniques. Since now, most of the reports on ZnO films on polymer substrates are dealing with sputter deposition processes and only few papers report on films deposited by PLD [52–56]. The process parameters (laser fluence ˚, gas background, substrate temperature, etc.) can be controlled independently in PLD. This enables to tune the chem- ical composition and the crystalline texture of films. The deposition rate in PLD is high compared to other vapor deposition techniques. Due to the high kinetic energy of species in the laser-induced plasma plume the films may be crystallized at lower substrate tem- perature [42,43]. The type of substrate material influences strongly the morphol- ogy of deposited films. The roughness of transparent electrodes is an important characteristics in the fabrication of organic solar cells due to short-circuits and/or leakage currents which can rise. 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.03.046