Synthesis of perovskite Cs 2 SnI 6 film via the solution processed approach: First study on the photoelectrochemical water splitting application Tran Chien Dang a , Ha Chi Le b, ** , Duy Long Pham b , Si Hieu Nguyen b , Thi Tu Oanh Nguyen b , Tien Thanh Nguyen b , Tien Dai Nguyen a, * a Institute of Theoretical and Applied Research, Duy Tan University, Hanoi 100000, Viet Nam b Institute of Materials Science, Vietnam Academy of Science and Technology,18 Hoang Quoc Viet, Cau Giay, Hanoi, Viet Nam article info Article history: Received 10 April 2019 Received in revised form 10 July 2019 Accepted 12 July 2019 Available online 12 July 2019 Keywords: Perovskite Cs 2 SnI 6 Annealing Solution processed approach Photoelectrochemical abstract We report on the synthesis of perovskite Cs 2 SnI 6 films via the solutioneprocessed approach. The cubic Cs 2 SnI 6 phase (Fm3m group) formed at the annealing temperature of 170  C for 8 h in air has uniform morphology. The optical characteristics of the compound depended on the annealing temperature and the compound behaved like a direct band gap semiconductor. Based on these findings, we firstly investigated the potential application of Cs 2 SnI 6 to photoelectrochemical (PEC) water splitting using a 0.3 M NaCl electrolyte. The photocurrent density (PCD) and photoconversion efficiency (h) were 0.92 mA cm 2 and 0.54% at 0.8 V, respectively. This might be suitable for fabricating the hybrid PEC device. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Recently, cesium tin iodide (CSI) perovskite semiconductor has been attracting much attention for solar cells, light emitting diodes, photodetectors, superconductivity, catalytic electrodes in fuel cells, and sensor applications due to the high efficiency, inexpensive cost and environmental friendly issue of device fabrication [1e 15]. The CSI system belongs to the perovskite semiconductor group with the orthorhombic structure at room temperature. This material has shown phase transitions due to the synthesis conditions (the ambient air, the annealing temperature and the solid-state or so- lution approach [16e20]). However, it has exhibited many inter- esting physical properties such as high composition stability of phases (yelloweCsSnI 3 and blackege CsSnI 3 of space group Pnma) [1 ,2], high hole mobility, low trap density, direct band gap behavior, large absorption coefficient. At present, the power conversion ef- ficiency (PCE) of Cs 2 SnI 6 material (E g ¼ 1.2e1.7 eV) has been improved to approximately 8% [20], 4.63%e6.94% for dye solar cells [17], and it is more thermally stable than ABI 3 etype (A ¼ Cs, CH 3 NH 3 ,C 2 H 4 N and B ¼ Pb, Sn) perovskite material structure [8,21]. To continue developing Snebased perovskite materials of nonetoxicity and longeterm stability and their solar cell devices of slow charge recombination and high energy conversion efficiency to avoid the toxicity of Pbebased halide perovskite materials, in this work, we synthesized Cs 2 SnI 6 compound under ambient air by solutioneprocessed approach. By manipulating temperature, the effect of annealing temperature on the crystalline structure, morphology and optical properties of CSI materials were investi- gated. Based on this result, we firstly studied the potential appli- cation of the Cs 2 SnI 6 material to photoelectrochemical (PEC) water splitting using a 0.3 M NaCl electrolyte. The results suggested that the hybrid structure might pave a novel approach for the next generated PEC device of the CSIebased material. 2. Experiment procedure Pristine CSI compound powder was synthesized by the solution processing approach. A mixture of 0.2054 g of CsI and 0.2946 g of SnI 2 (from Sigma Aldrich) was dissolved into 3 ml of N, Nedimethylformamide and acetonitrile with 3:2 vol ratio. Then, it was stirred for 12 h at room temperature (RT). The CsSnI 3 phase was * Corresponding author. ** Corresponding author. E-mail addresses: chilh@ims.vast.ac.vn (H.C. Le), nguyentiendai@duytan.edu.vn (T.D. Nguyen). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2019.07.122 0925-8388/© 2019 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 805 (2019) 847e851