Damp-heat treatment of Cu(In,Ga)(S,Se)2 solar cells

The influence of accelerated lifetime tests on solar cells and Schottky diodes based on Cu(In,Ga)(S,Se)₂ thin films is studied. We have analyzed the stability of non-encapsulated test cells in the standardized damp-heat (DH) treatment. The electrical changes of our samples due to DH testing are investigated using transport measurements (admittance spectroscopy (AS) and deep-level transient spectroscopy (DLTS)). We identify several defect states in the heterostructure. Two of them, a deep acceptor-like defect state and a deep recombination center, are related to the electronic changes induced by the DH treatment. In order to verify the spatial location of the majority-carrier traps, we separate the effect of DH on the absorber layer from that of the window and buffer layers by characterizing Cr Schottky contacts on as-grown and DH-treated Cu(In,Ga)(S,Se)₂ thin films. We find that the defect levels are located in the absorber layer. Another defect state observed in heterostructure cells, previously reported to be located in the vicinity of the buffer/absorber interface, is detected in the Schottky diodes as well.