Durability of ITO/Ag-Alloy/ITO Films on Pet Substrate Under Extended Bending Stress at Various Temperature and Humidity Conditions

Flexible electronic devices, such as OLEDs, flat panel displays (FPDs), and photovoltaic solar cells, frequently employ transparent conductive electrodes composed of indium tin oxide (ITO)/Ag-alloy/ITO-coated polymer films. However, the films are subjected to a combination of thermal and mechanical forces, particularly bending around rolls, during roll-to-roll manufacturing. This can result in thin film failure. Furthermore, these films are curved around the surface of flexible electronic devices, such as solar cells, during operation. Furthermore, they can be in service in hot and humid locations for extended periods throughout the summer, such as deserts. These stresses can lead to the degradation of the device’s performance by causing cracks in the conductive thin films and corrosion of the Ag-alloy layer over time.

In this work, ITO/Ag-alloy/ITO films were bent under tensile mode to different radius of curvature over a period of time at different humidity and temperature levels. The electrical resistance was measured in situ, and four combinations of temperature and relative humidity were used: 25°C, 65°C, and 25 percent and 80 percent. According to the results, irrespective of the temperature level, high humidity causes the films to degrade more quickly. Particularly, the films exhibited a notable increase in normalized electrical resistance when subjected to a 4.3 mm radius of curvature in both high temperature and high humidity conditions. This was associated to aggregation of the silver layer, film buckling, and crack formation. Furthermore, the film’s conductivity was further reduced by surface cracks that allowed oxygen and moisture to penetrate. Consequently, to maintain the integrity of the film, an external applied stress with moisture and/or harsh environments as well as moisture and/or harsh environments alone should be avoided during both manufacturing and application processes.