Evaluating TCO long-term performance by electrochemical corrosion test and residual film stress analysis

To evaluate the long-term performance of transparent conductive oxides (TCOs) in thin-film PV applications, electrochemical corrosion testing was carried out on three fluorine-doped tin oxide films on glass. The test assesses the TCO´s susceptibility to delamination in thin-film PV modules. One TCO tested passed the test and the other two failed the test due to delamination and cracking. An X-ray diffraction (XRD) technique was used to determine residual film stress of the TCO films. Compressive stress was found in all the TCO films. The lowest stress was at -723 MPa and the highest stress was at Ȓ1173 MPa. Films with higher residual stresses had more areas of delamination. It is proposed that sodium ions formed at the TCO/glass interface and water diffusion into the film from the electrochemical corrosion test initiate straight-sided blister formation or buckling. When the compressive residual stress in the film is high, buckling-driven delamination occurs. This work suggests that both the electrochemical corrosion test and the XRD film stress analysis may be useful methods to rank the long-term performance of TCOs.