The effects of various annealing regimes on the microstructure and physical properties of ITO (In 2 O 3 :Sn) thin ﬁlms deposited by electron beam evaporation for solar energy applications Antonia Sonia Alves Cardoso Diniz * Pontiﬁcal Catholic University of Minas Gerais (PUC Minas), Politechnical Institute (IPUC), Av. Dom José Gaspar, 500, Prédio 3, 30535-610, Belo Horizonte, M.G., Brazil article info Article history: Received 5 March 2009 Accepted 8 September 2010 Available online 25 October 2010 Keywords: Indium tin oxide Heat treatment Microstructure Electrical and optical properties abstract The goal of this study has been to investigate the inﬂuence of various post-deposition heat treatments on the microstructure, electrical and optical properties of In 2 O 3 :Sn (ITO) thin ﬁlms deposited by electron beam evaporation. We have shown that electron beam evaporated ITO thin ﬁlms deposited onto substrates kept upto 150  C, have poor electrical properties and low optical transmission in the visible range, due to their amorphous structure. As the microstructure changes from amorphous to poly- crystalline it was observed that the ﬁlm resistivity decreases and it is simultaneously related to an improvement in the optical transmission. From comparisons of several annealing processes it has been observed that oxygen plays an important role in doping as well as the presence of Sn in the target material. Furthermore we have shown that high quality ITO thin ﬁlms can be reproducibly prepared with optical transmission being enhanced by an annealing in air and the electrical characteristics being improved by a further annealing in a reducing atmosphere. Superior electrical and optical properties could be correlated with annealed ﬁlms that exhibited a cubic bixbyte structure and large crystallite dimensions larger than 50 nm. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Renewable and efﬁciency energies are seen as important players in addressing many of the top challenges facing the world to protect the environment. Addressing these challenges will require actions in several areas, including the development of new materials. Among those materials, the transparent conducting oxide (TCO) ﬁlms have been widely used for a variety of applications in efﬁ- ciency and renewable energy areas, due to a special compromise between their electrical and optical properties which is made to suit the speciﬁc application. They can be used as transparent front surface electrodes in solar cells [1e4] and energy efﬁcient windows [5]. They have also been employed in other applications, such as in infrared reﬂectors, heat mirrors, thin ﬁlm resistors and gas sensors [5,6]. Among the existing TCOs, Sn doped In 2 O 3 (ITO) is one of the most frequently used material. The technologically important properties of ITO (In 2 O 3 :Sn) ﬁlms are due to their unique combi- nation of electrical and optical properties. Indium tin oxide being a wide band gap material n-type semiconductor, exhibits high visible transmission. However, transparency and high electrical conductivity are, to some extent mutually exclusive. Good electrical properties can be achieved but often at the expense of optical transmission [1,2]. A large number of applications exist in which indium oxide and In 2 O 3 :Sn (ITO) ﬁlms are involved in active or passive roles, but the physical property requirements for the performance of the material vary with the particular application [1e6]. ITO ﬁlms can be deposited using a various set of methods such as sputtering, spray pyrolysis, electron beam evaporation, pulsed laser deposition, ion plating, screen printing and CVD [5,6]. Residual gas mass spectrometry measurements performed during and immediately after the evaporation of ITO, showed when ITO is evaporated, it decomposes slightly into suboxides and free oxygen and were strongly absorbing over the wavelength range from 0.2 mm up to 50 mm. The band gap of ITO is around 3.7 eV, which implies that the dark ITO suffers from midgap absorption. As a result in order to get reproducible ITO layers, it is clearly neces- sary to control the amount of oxygen in the ﬁlms [7e9], which can be achieved by oxidation of the target during deposition or by post- deposition heat treatments [8e17]. In spite of the technological importance of ITO thin ﬁlms much of the literature on ITO ﬁlms relate to studies of the dependence of * Tel./fax: þ55 31 3319 4910. E-mail address: asacd@pucminas.br. Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2010.09.005 Renewable Energy 36 (2011) 1153e1165