Abstract
Surface instability via wrinkle formation is a common feature in thin films attached to a compliant substrate. Wrinkled thin-film structures have been increasingly exploited to enhance device performance. In this study a numerical technique utilizing embedded imperfections is employed for direct simulations of wrinkle formation, extending from a single-film structure to composite films involving two or more layers. The incorporation of material elements, bearing different elastic properties at the film-substrate interface, assists in triggering buckling instability when the compressive strain reaches a critical value. The wrinkle wavelength and amplitude obtained from the numerical modeling show excellent agreements with available theoretical solutions involving bi-layer composite films, over the entire span of volume ratios of the constituent layers. A valid range of imperfection distribution, resulting in uniform wrinkle formation, is identified. The current numerical approach is robust and easy to implement and yields great promises in generating reliable wrinkling patterns. It can be readily applied to cases where realistic features cannot be captured by theories, such as the generalized plane strain deformation, indirect compression, and multilayer composite films.
Highlights
Surface instability in the form of wrinkle formation is a common feature in thin films attached to a compliant substrate
For the case of bilayer thin films on top of a compliant substrate, we focus on the analytical solutions where wrinkling of the two films occurs in tandem (Jia et al, 2012), which is of direct relevance to the present work
A comprehensive numerical study was conducted for simulating surface instability in the form of wrinkles, when a thin-film material is attached to a thick compliant substrate
Summary
Surface instability in the form of wrinkle formation is a common feature in thin films attached to a compliant substrate. In polymer-based photovoltaic (PV) and optoelectronic systems, surface wrinkling is increasingly exploited to enhance the device performance. In the case of “hard” PV and/or conducting layers such as silicon, perovskite, and indium tin oxide, various ways of fabricating them onto an instability-driven wrinkled base structure, for the purpose of enhancing light trapping (Ram et al, 2017; Bush et al, 2018; Schauer et al, 2018; Zhang et al, 2018) or scattering (Wang C. et al, 2017), have been reported. An added benefit of the wrinkled structure is the possible improvement in deformability in stretchable electronics (Wang B. et al, 2017); enabling their potential deployment in fabrics and on curved or uneven surfaces. Wrinkling instabilities have been reported for dielectric elastomers (Zhu et al, 2012; Zurlo et al, 2017)
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