Effects of cyclic deformation on a barrier thin film for flexible organic optoelectronic devices

Effects of cyclic bending on the encapsulation properties of a barrier thin film are investigated. Water vapor transmission rate (WVTR) of the given barrier film is measured after variously cyclic bending conditions using a calcium corrosion test technique. Experimental results show that microcracks in the barrier thin film are found after applying a certain number of bending cycles. They are responsible for an increase in WVTR. Given a bending radius, a greater number of bending cycles leads to a larger amount of damage, and consequently a greater extent of moisture ingress. A smaller bending radius produces a greater amount of damage than a larger one, in a short period of loading time (≤104 cycles). However, after 105 cycles of cyclic bending, the amount of damage reaches a saturated level regardless of bending radius, as all the WVTR values become comparable. A simplified 3D finite element analysis (FEA) model is established in microscale to analyze the moisture diffusion mechanism. Numerical results show that, with the presence of cracking and delamination, the WVTR value increases significantly. Good agreement between the simulation and experimental measurements on WVTR confirms that the failure mechanism involves cracking and delamination under cyclic bending. The 3D FEA modeling developed could offer a method to predict the change of WVTR in correlation with cracking and delamination in the barrier thin film.