AE Monitoring of Damage Accumulation in Transparent Conductive Oxide Film under the Mechanical Strain

Abstract

In this study, tensile tests of the transparent conductive oxide (TCO) deposited on the polyethylene naphthalate (PEN) films (TCO + PEN films) used in dye-sensitized solar cells (DSCs) were carried out. In order to discriminate the AE signals in TCO from PEN films, PEN film specimens (TCO was removed by 17.5% hydrochloric acid) were also prepared. It was found from the tensile tests that many AE signals were detected in TCO + PEN films, while AE activity in PEN films was much lower. On the other hand, the electric resistance of TCO was also measured during tensile tests. The remarkable increase in AE event rate was recognized at the strain of ∼0.63%, while the electric resistance increased rapidly at the strain of 0.68%. These results demonstrated that the critical damage in TCO was detected by the measurement of AE signals more sensitively than the electric resistance measurement. To identify AE sources, in-situ observation of specimen during tensile test with AE measurement was carried out. During tensile test, cracks transverse to the loading direction in the TCO were found at the strain of 0.67%, and then saturated at the strain of ∼9%. Cracks parallel to the loading direction in TCO were initiated at the strain of 9.63%. On the other hand, the remarkable increase in AE event rate was recognized at the strain of ∼0.7%. It reached a peak at the strain of ∼2%, and then decreased, and increased again at the strain of ∼10%. It was then concluded that AE behavior corresponds to the cracking behavior in TCO. Consequently, it was suggested that AE technique could be a powerful technique for evaluating the damage accumulation process in DSCs.