Effect of the absorber layer band-gap on CIGS solar cell

The efficiency of Copper Indium Gallium Diselenide solar cell has been steadily increasing over this last decade to reach a record value of 21.7% by the year 2014 complemented with a noticeable cost reduction. The observed improvement in performance could be attributed to the advance in growth and production techniques bringing forth best quality CIGS thin-films. The most attractive property of CIGS compound is the ability to tune its energy band gap from 1.01 eV up to 1.68 eV by variation of Ga fraction leading to a best match to the solar spectrum. In the present work we demonstrate the improvement to be gained if the CIGS band gap is optimized. First, the energy band gap of CIGS absorber layer was varied uniformly to find the optimal Ga content. The simulation is carried out using the solar cell simulator SCAPS-1D. It is found that maximum efficiency of about 22.95% can be achieved with a band gap of around 1.48 eV. In the second set of investigations, a graded band gap absorber is examined. In this simulation several configurations were examined the maximum efficiency obtained is 24.34%.