Tikrit Journal of Pure Science Vol. 24 (3) 2019 77 Tikrit Journal of Pure Science ISSN: 1813 – 1662 (Print) --- E-ISSN: 2415 – 1726 (Online) Journal Homepage: http://tjps.tu.edu.iq/index.php/j Study effect of window and BSF layers on the properties of the CZTS / CZTSe solar cell by SCAPS–1D Alaa H. Najim , Ayed N. Saleh Department of physics , Collage of Education for pure science , Tikrit University , Tikrit , Iraq DOI: http://dx.doi.org/10.25130/tjps.24.2019.050 A r t i c l e i n f o. Article history: -Received: 30 / 9 / 2018 -Accepted: 12 / 11 / 2018 -Available online: / / 2019 Keywords: SCAPS-1D, CZTSe, CZTS, transition metal oxides (TMO), Back surface field (BSF), solar cell, conversion efficiency (), fill factor (FF), Quantum efficiency (QE). Corresponding Author: Name: Ayed N. Saleh E-mail: ayed.ns@tu.edu.iq Tel: ABSTRACT The solar cell CZTS / CZTSe was studied using SCAPS-  computer simulator. It was noted that increasing the thickness of the absorber layer p-CZTSe from 250nm to 5μm leads to increase the IV curve. thus increasing the values of Voc, Jsc, FF,  up to 0.79 Volt, 39.35 mA/  , 85.92% and 26.8% respectively, and optical properties of Quantum efficiency (QE) increased from 54% to 95%. The addition of the transition metal oxides (TMO) to the cell showed that the oxides (Ti  , Sn  , ITO, FTO) had the highest conversion efficiency among the other oxides at 25.63% and this value increased by increasing the thickness of the absorption layer to 29.32%. In addition to the BSF of the cell ,   eTdC - , SnS, had the highest conversion efficiency of 33.75% and 29.64%, respectively. The thickness of the absorption layer increased the conversion efficiency value from 13.16% at 250nm to 33.9 5% at 5µm for   – , and from 10.27% to 29.89% for SnS, While the value of the fill factor (FF) is reduced from 69.93% at 250 nm to 61.01% at 2 μm for   – , and at most constant value at 85 % for SnS. By combining these compounds from the transition metal oxides and the Back surface field with the CZTS / CZTSe cell, Can get six cells with conversion efficiency values ranging between 33.82% and 29.71%, and the change in these values can affect the thickness by change the thickness of the absorption layer. For quantum efficiency, their value is increased to 100% by the rise in the absorption layer thickness to 5μm because cells are ideal . Introduction Solar cells are photovoltaic devices that convert electromagnetic radiation (i.e. light, including infrared, visible and ultraviolet radiation) from the sun to usable electrical energy. Solar cells are used in various terrestrial and space applications, as they can convert solar energy directly into electrical energy, with good conversion efficiency, and can produce near-constant capacity, low operating costs and no pollution in the environment [1]. The study of binary compounds has increased the creation of new materials for solar cells. The research has focused on thin film solar cells for high efficiency and relatively low cost. Currently, the semiconductors Cu2ZnSnSe4 (CZTSe), Cu2ZnSnS4 (CZTS) and their alloys   ZnSn (    ) 4 with the direct power gap between (1-1.5 eV) attract attention [2]. Because they contain abundant and safe elements such as Zn and Sn, and the coefficient of absorption of the thin film CZTSSe is large enough )      (.The highest efficiency of the CZTSSe cell achieved so far is 12.7% where it is still far from the theoretical calculations. It is also required to understand and fully control the various manufacturing processes and interactions in order to obtain high efficiency [3]. The aim of this study is to show a high efficiency of the CZTS / CZTSe cell using the computer simulation method of solar cells in addition to studying the effect of the transition metal oxides (TMO) on the cell and the extent of their interaction with different types of these oxides to choose the best ones in terms of efficiency in addition to the use of different types of Back surface field (BSL) to see how they affect the cell.