Electrical and Optical Degradation Studies on AZO Thin Films Under Cyclic Bending Conditions

Aluminum-doped zinc oxide (AZO) thin film is a promising candidate for low-cost transparent conductive oxide applications. AZO thin films have good electrical and optical properties; however, their reliability must be carefully considered in manufacturing and usage of flexible devices such as flexible solar cells. Cyclic bending leads to both electrical and optical degradation of AZO thin films. Therefore, this paper was designed to investigate the effects of the bending frequency, bending diameter, number of bending cycles, and film thickness on the electrical and optical degradation of AZO films, which were deposited on polyimide (PI) substrates using a radio frequency-magnetron sputtering technique. The cycling was conducted on identical specimens under controlled study parameters. The design of experiments technique was used to determine the significant factors on the percentage change in electrical resistance (PCER) and the degradation of average transmittance (DAT), considering a wavelength range from 660 to 950 nm. The result shows that the PCER is very sensitive to number of bending cycles, particularly in the first 300 cycles. After 1000 cycles, the mean PCER of 425- and 600-nm AZO films are about 300% and 600%, respectively. The DAT is sensitive to number of bending cycles, bending diameter, and bending frequency. The mean DAT is about 2.8% after 1000 bending cycles.