Compositional grading of CZTSSe alloy using exponential and uniform grading laws in SCAPS-ID simulation

• Published in: Superlattices and microstructures 2016-04, Vol.92, p.285-293
• Main Authors: Simya, O.K., Mahaboobbatcha, A., Balachander, K.
• Format: Article
• Language: English
• Subjects: Band-gap; CZTSSe; Exponential law; Grading; Photovoltaic cells; SCAPS-ID; Selenium; Simulation; Solar cells; Sulfur; Sulphur; Uniform law; Zinc oxide
• ISSN: 0749-6036; 1096-3677
• DOI: 10.1016/j.spmi.2016.02.019

The SCAPS (Solar cell capacitance simulation) program were employed to analyze the compositional dependence of CZTSSe (Copper Zinc Tin Sulphur Selenium) absorber layers with Cadmium Sulphide (CdS) as buffer layer and Zinc Oxide (ZnO) as window layer for thin film solar cells applications. The primary motivation of this simulation work is to optimize the composition for Se/(S + Se) ratio, which would yield higher efficiency. The exponential and uniform grading law in SCAPS were set for the composition grading y(x) over a layer, as well as to set the composition dependence P(y) of a property. By varying the different compositions with exponential law and by using uniform law for the same composition, best efficiency of 14.97% were achieved for 0.4–0.1 composition of sulphur and selenium with Se/(S + Se) ratio of 0.80. Higher efficiency were obtained with higher Se content. The influences of the band gap of the CZTSSe alloys, which decreases linearly with an increase in its Se content, were further analyzed. The corresponding open circuit voltage, short circuit voltage, fill factor and efficiency of the simulated values on a photovoltaic cell with Mo back contact were studied in detail. •Compositional Grading using exponential and uniform law in SCAPS.•Bandgap tuning mainly depends upon the Se/(S + Se) ratio.•The best efficiency of 14.97%, were achieved for 0.4–0.1 composition of sulphur and selenium with Se/(S + Se) ratio of 0.80.•The open circuit voltage (Voc) increases when there is a decrease in its short circuit current (Jsc).•Increased Voc decreases the built-in electric field in the SCR region of absorber layer, which in-turn decreases the FF.