Solar Energy Materials & Solar Cells 91 (2007) 864–870 Electrodeposited zinc oxide thin films: Nucleation and growth mechanism A.I. Inamdar, S.H. Mujawar, S.B. Sadale, A.C. Sonavane, M.B. Shelar, P.S. Shinde, P.S. Patil à Thin Film Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416 004, India Received 7 September 2006; received in revised form 28 November 2006; accepted 31 January 2007 Available online 13 March 2007 Abstract The nucleation and growth mechanism of the electrodeposited zinc oxide thin films on fluorine-doped tin oxide (FTO) coated (10–20 O/cm 2 ) glass substrates from acetate solution, without and with ex situ oxygen bubbling, has been studied by cyclic voltammetry (CV), chronoamperometry (CA) and scanning electron microscopy (SEM) techniques. Ethylene diamine tetra acetic acid (EDTA) was used as a complexing agent. The cyclic voltammograms exhibit crossover, a characteristic of nucleation process on FTO-coated conducting glass substrates for all the baths bubbled with oxygen. The current transients were analyzed by fitting chronoamperometric data into the Scharifker–Hills nucleation model. The plausible nucleation and growth mechanism is proposed. For mother bath and lower oxygen bubbling time, the nucleation and growth mechanism follows 3D progressive nucleation and growth, which became instantaneous in case of baths for higher oxygen bubbling time. The SEM study showed that the films become compact when the oxygen bubbling time was increased. The thin films were further characterized by X-ray diffraction technique for structural studies and the ZnO film formation was confirmed. With the increase in oxygen bubbling time, the shift in band gap energies from 3.2 to 3.3 eV is observed. r 2007 Elsevier B.V. All rights reserved. Keywords: Zinc oxide thin films; Electrodeposition; Cyclic voltammetry; Chronoamperometry; Scanning electron microscopy (SEM); X-ray diffraction 1. Introduction Zinc oxide (ZnO) is a direct wide band gap (3.3 eV) semiconductor with large exciton binding energy of 60 meV at room temperature. It has various applications in optical, electrical and acoustic devices like UV lasing [1–3], optoelectronics [4], photovoltaics, photoconductive sensors and piezoelectric transducers [5]. In photovoltaics, they have been used as transparent conducting electrodes in solar cells based on copper indium diselenide [6] or amorphous silicon [7] absorbers. The ultraviolet lasing of bulk ZnO material has been demonstrated at cryogenic temperature many years ago [8]; potential applications of ZnO nanostructures include UV lasing [9,10], electroop- tical switch [4] and hydrogen storage [11] devices. Several studies have been devoted to the electrodeposi- tion of ZnO thin films directly from oxygen-dissolved precursor, as for instance for cathodic deposition using nitride ions as the oxygen precursor [12]. It has been discovered that good quality zinc oxide thin films can be deposited simply using dissolved oxygen as the precursor [13,14] according to overall reaction. Zn 2þ þ 0:5O 2 þ 2e  ! ZnO: (1) Various other techniques have also been used to deposit ZnO thin films such as sputtering [6], metal-organic chemical vapour deposition [15], molecular beam epitaxy and atomic layer epitaxy [16]. The effect of polyehoxylated additives and organic additives on zinc electrocrystalli- zation and on their kinetic parameters was studied by Trejo and Alvarez et al. [17,18]. Peulon and Lincot [13,14] described the cathodic electrodeposition of ZnO thin films from oxygenated aqueous zinc salt solution. The effect of oxygen concentration on morphology and on deposition parameters was studied by Pauporte and Lincot [19]. The nucleation and growth mechanism of electrosynthesized ARTICLE IN PRESS www.elsevier.com/locate/solmat 0927-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2007.01.018 à Corresponding author. Tel.: +91 231 2690571; fax: +91 231 2691533. E-mail address: psp_phy@unishivaji.ac.in (P.S. Patil).