IntroductionAs compared to Cu-chalcopyrite, CdTe and amorphous Si thin film solar cells, copper-indium-gallium-diselenide (CIGS)thin film solar cells has achieved the highest conversion efficiency [1,2]. The driving forces for CIGS are compelling: potentiallyhigh efficiency and low specific energy for production [3]. In order to optimize the CIGS thin film solar cells performances andimprove the metastable electronic behavior of these solar cells, one should first improve the quality of the CIGS absorberlayer [4,5] and then that of the interface between CIGS and buffer and window layers [6,7]. Generally, record cells andindustrial modules are equipped with a thin CdS buffer modifying the p/n junction between the p-type absorber and then-type window, usually ZnO [8]. A number of alternatives to CdS buffers exist. However, chalcopyrite solar cells employingalternative buffers can reach the same efficiencies as those with CdS buffers. Moreover, in some cases it is observed thoughthat these alternative buffers are more prone to metastable effects like light soaking and show somewhat less stability indamp heat testing [8].