Elucidating the Effect of the Different Buffer Layers on the Thermal Stability of CIGSe Solar Cells

In this contribution, the impact of thermal stress on Cu(In,Ga)Se
₂
(CIGSe) thin film photovoltaic devices is investigated. The tolerance of such devices to high temperatures is of particular interest for processing transparent conductive oxides (TCOs) in order to further close the gap to the theoretical efficiency limit and for their potential use as bottom devices in tandem applications in order to overcome the theoretical efficiency limit of single junction solar cells. When CdS-buffered CIGSe high efficiency solar cells are subjected to thermal stress, elemental interdiffusion of Na and Cd between the absorber and the window layers as well as chemical reactions at the CIGSe/CdS interface result in a degraded power conversion efficiency (PCE). Here, we compare the degradation mechanisms of CdS and GaO
_x
buffered CIGSe solar cells under thermal stress. A model explaining the observed degradation behaviors is proposed.