Tikrit Journal of Pure Science Vol. 25 (2) 2020 71 Tikrit Journal of Pure Science ISSN: 1813 – 1662 (Print) --- E-ISSN: 2415 – 1726 (Online) Journal Homepage: http://tjps.tu.edu.iq/index.php/j Simulation of CZTSSe single solar cells by AFORS-HET software Buthina M. Jandary , Ayed N. Saleh Physics Department , College of Education for pure science University of Tikrit , Iraq DOI: http://dx.doi.org/10.25130/tjps.25.2020.032 A r t i c l e i n f o. Article history: -Received: 23 / 9 / 2019 -Accepted: 29 / 11 / 2019 -Available online: / / 2020 Keywords: Cu 2 ZnSn(SSe) 4 , thin- film solar cell, numerical modeling, AFORS-HET software. Corresponding Author: Name: Buthina M. Jandary E-mail: buthina088@gmail.com Tel: ABSTRACT In this paper, this sthdy simulated photovoltaic characteristics of single heterojunction solar cell with Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 absorber layer numerically using the AFORS-HET program .n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different absorption layer properties such as thickness, carrier concentration. The mixed zinc and cadmium sulphide (Cd 1-X Zn X S) is hired as buffer layers and reseach of the effect its thickness. CdS was selected a buffer because it improves the interface with absorbent CZTSSe and has a lofty sending in the blue wavelength. at thickness =1 μm and acceptor concentration (Na=7.9×10 15 cm -3 ) ,a maximum efficiency (η=11.9%) is provided with an open-circuit voltage (Voc=688mv), short-circuit current (Jsc=24.6 mA.cm-2) and fill factor (FF =70.8 of the CZTS solar cell, and Voc=(597 mv), Jsc= (41.7mA.cm-2), FF = (81.2 %) and η= (20.2%) of the CZTSe solar cell. 1- Introduction The photovoltaic (PV) system, known today as renewable, clean, and sustainable have attracted much interest because of the following advantages: First, photovoltaic systems able of converting sunlight directly into electrical energy. Second, theoretical efficiency of photovoltaic system is relatively higher than the energy sources other. Third, photovoltaic cell technique not contain moving parts, which prevents corrosion of the system resulting from mechanical movement were PV system work continuously without maintenance [1]. Today, researchers are interested in exploring and developing new, cost-effective and abundant materials in the earth, such as semiconductors Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 [Cu 2 ZnSn(SSe) 4 (CZTSSe)] ,whose compounds are widely studied as absorption layers for thin-film solar cells [2]. due to its potential as a future absorber material for high efficiency thin film solar cell technology. The properties such as environmentally benign and earth a bundant constituent elements, optimum direct bandgap (1- 1.5eV) and high absorption coefficient (α >10 4 cm - 1 ), ( thickness of 1 micrometer is enough to absorbare most of the falling sunlight) , make CZTSSe a material of choice as an alternative to the existing solar photovoltaic thin film technologies [3] ,Where the process of production of this compound is cheaper compared to the bsorption of CdTe and CIGS,as shown in Fig 1. Fig 1: The cash cost of producing the absorption layers [4] One of the greatest features of the Cu 2 ZnSn(SSe) 4 compound is the possession of a direct band gap and easy to change which depends on the material composition by controlling the contents of S and Se [5]. Band gap varies with the ratio (S) and (S + Se) of about 1.0 eV in Cu 2 ZnSnSe 4 (CZTSe) to 1.5 eV in Cu 2 ZnSnS 4 (CZTS). Recent research shows that the S / Se variation does not only result in variation of the band gap, but also changes the electronic structure, absorption coefficient, and other parameters such as electron affinity and dielectric permittivity, etc .