Numerical analysis on compositional grading of CIGS thin film solar cells with a double graded bandgap absorber using parabolic and exponential grading laws
This study demonstrates an innovative CuIn1-xGaxSe2 (CIGS)-based solar cell model with a double graded bandgap absorber profile, capable of achieving high efficiency. This paper presents an in-depth discussion concerning the potential improvement in electrical characteristics of CIGS solar cell by bandgap grading. Bandgap grading can be accomplished through variation of Gallium (Ga) composition as a function of thickness across the absorber layer, and double grading profile has been proven to be the most effective. SCAPS software is used in order to numerically simulate the cell electrical behaviour. Two different grading laws that can be implemented in the grading structure; namely exponential and parabolic methods, as well as the variation of relevant parameters, are studied by means of simulation. Based on this analysis, it is shown that cell with an optimized parabolic type of double graded bandgap structure surpasses the exponential type with open-circuit voltage (VOC) of 0.855 V, short-circuit current density (JSC) of 39.38 mA/cm2, fill factor (FF) of 76.08% and power conversion efficiency (PCE) equal to 25.63%.