The impact of reducing the thickness of electrodeposited stacked Cu/In/Ga layers on the performance of CIGS solar cells

In this work, Cu(In,Ga)Se₂ (CIGS) absorbers with thicknesses ranging from 2 µm to 370 nm were prepared by a two-step process using electrodeposition of Cu-In-Ga followed by annealing under a pure Se atmosphere. Based on compositional characterizations, it is shown that in order to decrease the thickness of the precursors, it is not enough to reduce only the deposition time of Cu-In-Ga layers without working on the composition and deposition parameters of the thin films. After the optimization of annealing conditions, the properties of the absorbers and solar cells with three different thicknesses (2 µm, 0.7 µm and 0.37 µm) were compared. It is shown that, in spite of the decreasing thickness, hence a decrease in J_SC, the V_OC of ultrathin CIGS electrodeposited solar cells can be improved due to an increase in the Ga content of the electrodeposited absorbers. Without deliberate light trapping and anti-reflecting coating from the very thin absorber layer of 0.37 µm, an efficiency of 8.7% with V_OC of 685 mV, J_SC of 19 mA/cm² and FF of 67%, was achieved.