IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 11, Issue 2 Ser. II (Mar. – Apr. 2019), PP 74-81 www.iosrjournals.org DOI: 10.9790/4861-1102027481 www.iosrjournals.org 74 | Page Electronic Band Structure of Copper Zinc Tin Sulphide (Cu 2 ZnSnS 4 ). 1 Nwachuku D.N. & 2 Omehe N.N 1. Physics department, College of Education, Agbor Delta State, Nigeria. 2. Physics department, Federal University, Otuoke, Bayelsa State, Nigeria. Corresponding Author: Nwachuku D.N Abstract: Cu 2 ZnSnS 4 (CZTS), made entirely of abundant materials, has attracted a great interest due to its potential applications in sustainable thin-film solar cell devices. The electronic band structure of kesterite Cu 2 ZnSnS 4 compound has been calculated using the pseudo-potential method. Projector augmented waves (PAW) within the density functional theory (DFT) was used in all calculations using local density approximation (LDA) for one calculation and inclusion of potential correlation term, U to LDA (i.e LDA + U) in another calculation. The results predicted Cu 2 ZnSnS 4 to be a p-type semiconductor with bandgap value for (1) LDA as 0.039 eV and (2) LDA + U as 1.83 eV. This bandgap value of 1.83 eV is in agreement with experimental results and it confirmed the material as a good absorber layer for solar cells. The density of states (DOS) showed that the conduction band was mainly contributions from Sn-5p and Zn-4s orbitals. It is recommended that the orbital independent term, U be added to LDA during calculations because it improves the bandgap value. Keyword: Cu 2 ZnSnS 4 , band structure, band gap, density of states. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 27-03-2019 Date of acceptance: 11-04-2019 --------------------------------------------------------------------------------------------------------------------------------------------------- I. Introduction Power generation through photovoltaics (PV) has been growing every year over the last decade by means of solar cells. Solar cells are classified into first-generation, second-generation and third-generation. The first-generation solar cells are based on silicon wafers. Silicon is still used extensively in solar cell devices, even though it has many limitations, such as silicon not being an efficient material because of its indirect bandgap which leads to low efficiency of absorption of solar radiations in visible and near infrared [1]. Although, it is expensive but its extensive use can be attributed to the fact that silicon technology was among the first at the time of development of PV devices [2]. The second-generation solar cells are less material intensive and avoid the use of silicon wafers. They have lower manufacturing costs. These include devices based on amorphous- silicon, CdTe, CulnS 2 and Cu(ln,Ga)(S,Se). However, these solar cells have several shortcomings based on their potential environmental hazard issues and scarcity [3]. Recently research trends are moving toward finding alternatives based on earth-abundant and non-toxic elements for fabricating solar cells. These are the third- generation solar cells. All solar cells are based on semiconductors and they convert radiation into electricity. Cheaper and potentially more cost-effective materials are formed by replacing In (III) with Zn (II) and Ga (III) with Sn (IV) in Cu 2 lnGaS 4 (CIGS) to give Cu 2 ZnSnS 4 (CZTS), because In and Ga are expensive and rare metals. This interesting I 2 -II-IV-VI 4 group semiconductor has great potential with a useful bandgap of 1.4 – 1.5 eV, a large absorption coefficient of over 10 4 cm -1 and is devoid of notably toxic or expensive elements [4]. CZTS is a heavy-fermion quartenary compound characterized by kesterite or stannite structure. It belongs to the family of semiconductor chalcogenide composition containing only non-toxic and earth-abundant elements, and hence it is widely used in developing environmental sustainable processes and devices such as solar cells and optoelectronics [5]. The crystallographic structure of kesterite Cu 2 ZnSnS 4 is shown in figure 1.