Air-annealing of Cu(In, Ga)Se 2 /CdS and performances of CIGS solar cells

In this study, the annealing treatment on Cu(In, Ga)Se2 (CIGS)/CdS interface in air is systematically investigated under different annealing temperatures from room temperature to 150 °C and different durations. It is found that when CIGS/CdS interface is annealed for a proper duration the corresponding CIGS thin film solar cells show enhanced open circuit voltage (Voc) and fill factor (FF) as well as corresponding conversion efficiency. The capacitance-voltage (C-V) and time-resolved photoluminescence (TR-PL) measurement results indicate that the CIGS thin film solar cells exhibit an increase in net defect density (NCV) and long lifetime for the carriers, respectively, after the annealing treatment of CIGS/CdS at a mediate annealing temperature here. Moreover, the net defect density of annealed solar cells at higher annealing temperatures for a long duration is reduced. All the variations in the solar cell performances, NCV and carrier lifetime would be related to the passivation of Se vacancies and InCu defects, surface (interface) states as well as positive interface discharges and Cu migration etc. A high efficiency CIGS solar cell of 14.4% is achieved. The optimized solar cell of 17.2% with a MgF2 anti-reflective layer has been obtained.