Optimization of Copper Indium Gallium Di-Selenide (CIGS) based solar cells by back grading

We performed modeling and simulation of Cu(In, Ga)Se₂ (CIGS) thin film solar cell, using SCAPS-1D device simulator, and we especially investigated the influence of absorber back surface region grading. The band-gap in the back surface region, as well as the thickness of the back surface grading layer, were varied to achieve the optimal performances. Based on these results, an optimal back-grading structure for Cu(In, Ga)Se₂ solar cell is proposed. It is shown that, the short-circuit current density (J_sc) improves with increasing the absorber band-gap in the back surface region. Very high J_sc of 32.72 mA/cm² was obtained, when the band-gap of the absorber near the back contact is 0.2 to 0.5 higher than the absorber bulk band-gap. The Open-circuit Voltage (V_oc), the fill factor (FF) and the efficiency (η) of the solar cell decrease for high band-gap near the back contact. The efficiency and the fill factor obtained for our model are respectively 16% and 75%. A comparison with published data for the Cu(In, Ga)Se₂ cells shows an excellent agreement.