Modeling and simulation of a front graded band gap CuInGaSe2 solar cell

In this work, a front graded band gap of CIGS absorber is simulated where a spatial variation of the band gap energy decreases from a maximum value E
gmax
at the limit of the junction to a minimum value E
gmin
at the vicinity of the back contact within the length of the CIGS layer. An effective absorption coefficient due to this variation was defined. It will be seen that this graded profile contributes to improve the open circuit voltage Voc owing to the effect of the created quasi-electrical field on the photo generated carriers which lead to an improvement of the efficiency. However, a reduction of the short current density J
sc
is noted. We also demonstrate that the absorber thickness has an impact on the parameters above mentioned. This simulation allowed us to optimize the grading profile which consists on E
gmin
, E
gmax
and the absorber thickness d in order to reach a desired significant improvement of V
oc
and efficiency.