Fig. 2. SEM images of: a) sample A, b) sample B. Surfactant-assisted Hydrothermal Synthesis of ZnO nanoflakes for perovskite Solar Cell applications E.Halvani anarakia*, A. Kermanpura, T. Zargar a  a Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran. *e.halvani@ma.iut.ac.ir Solar power as a clean and economical energy source plays an important role in the 21st century in a low greenhouse gas future. A new PEG-assisted zinc oxide (ZnO) crystal growth were successfully done through a simple hydrothermal method for perovskite solar cells. Formation of ZnO wurtzite crystal structure and average crystallite size of 28.7 (before calcination) and 31.9 nm (after calcination) was proved according XRD patterns. The uniform coating of nanoscale flake-like ZnO particles with average diameters of 276 and 250 nm were confirmed through SEM for non-calcined and calcined one, respectively. Keywords:“ZnO nanoflakes”; “Surfactant-assisted Hydrothermal method”; “Perovskite solar cells”. Introduction Results ZnO shows different physical and chemical properties depending upon the morphology of its nanostructures [1]. ZnO 0D, 1D, 2D and 3D nanostructures with different morphologies such as nanoparticles, nanorods, nanosheets and nanotetrapods have been used in solar cells [2]. Not only various synthesis methods but also the physical and chemical properties of synthesized zinc oxide are to be investigated in terms of its morphology [1]. The hydrothermal technique is attractive for synthesis ZnO nanostructures simplicity and environment friendly conditions [3]. Different studies were shown that may achieved to various morphologies of ZnO nanostructures with changing in every parameter of hydrothermal method such as pH of solution environmental, either using or not using surfactant, time and temperature [3-5]. XRD: In the XRD all the diffraction peaks of two samples are well indexed to the hexagonal ZnO wurtzite structure. The peak intensity of sample B decreases with calcination indicating decreased crystallinity, thus hydrothermal method doesn’t need any further calcination. The average crystallite sizes of the A and B samples are 28.7 nm and 31.9 nm, respectively. SEM: Fig. 2. SEM images of: a) sample A, b) sample B. The morphology of ZnO didn’t change with calcination. On the other hand the agglomerations of sample A are almost less than the agglomerations of sample B. The mean thickness of nanoflakes of samples A and B are 30 nm and 27 nm, respectively. The average nanoflakes diameter are 276 nm and 250 nm for samples A and B, respectively. Thus the calcination of products of hydrothermal method were maked to decrease the average sizes of nanoflakes. Fig. 1. XRD pattern of a) sample A and b) sample B. Materials and Method Materials: All raw materials, including Zn(NO3)2, NH4OH 25% , polyethylene glycol (PEG, MW = 6,000), n-butanol, methanol, chloroform were purchased from Merck Co. with minimum purity of 99%. Method: To synthesize ZnO nanoflakes, 2 g of Zn(NO3)2 were dissolved in 50 ml of double distilled water. The produced solution was continuously stirred by a magnetic stirrer. Then a solution of NH4OH 25% was added dropwise to reach a pH medium of 7.5. Vigorous stirring continued until a white slurry was formed. Then, 0.1 g of PEG was then added to the mixture and it was stirred vigorously for 1 h at room temperature and then transferred into a 325 ml volume teflon-lined. The autoclave was kept at 130 °C for 7 h and then free-cooled to room temperature. For powder characterization, the precipitate dried at 80ºC. The calcination of coated films was done at 300 ºC for 2 h. first sample, without calcination, was called A, and second sample, with calcination, was called B. References [1] S. Siva Kumar, P. Venkateswarlu, V. Ranga Rao, G. Nageswara Rao, “Synthesis, characterization and optical properties of zinc oxide nanoparticles”, Journal of International Nano Letters, 2013, doi:10.1186/2228-5326-3-30. [2] M.D. Tyona, R.U. Osuji, F.I. Ezema, “A review of zinc oxide photoanode films for dye-sensitized solar cells based on zinc oxide nanostructures”, Journal of Advances in Nano Research, 1 (2013) 43-58. [3] S. Baruah, J. Dutta, “Hydrothermal growth of ZnO nanostructures”, Journal of SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 2009, doi:10.1088/1468-6996/10/1/013001. [4] u. Zhou, W. Chen, L. Xu, S. Peng, “Hydrothermal Synthesis of Various Hierarchical ZnO Nanostructures and Their Methane Sensing Properties”, Journal of Sensors, 13( 2013), 6171-6182. [5] K. Byrappa, T. Adschiri, “Hydrothermal technology for nanotechnology”, Journal of Progress in Crystal Growth and Characterization of Materials, 53 (2007) 117-166.