Structural Innovations in Printed, Flexible, and Stretchable Electronics

Abstract

Research in stretchable, printed electronics combines multidisciplinary, state‐of‐the‐art developments in material science and structural engineering. In addition to major advances based on developing novel materials and fabrication processes, synergistic structural innovations are of equal importance for enabling stretchability in printed devices and should not be overlooked. Planar printing techniques are preferred, compared to microfabrication or 3D printing processes, owing to their low cost, high throughput, and compatibility with a wide range of materials. Various printing strategies for controlling the substrate, bonding, distribution of strain, and buckling can be used to fabricate a variety of devices featuring wrinkled, textile‐embedded, serpentine, island‐bridge, or 2D‐transformed 3D and 4D structures. Such structural innovations allow the use of ordinary printable materials for creating highly stretchable devices with minimal compromise in device performance and mechanical resiliency. This article provides an overview of the structures used in printed devices and summarizes their corresponding fabrication strategies and distinct features. The challenges of advancing the structural designs in printed devices and the prospects of transforming stretchable structures toward smart, responsive devices are also discussed. Future efforts will greatly expand the possibilities of using planar printing processes for fabricating complex structures with new functionalities.

Fluid‐Dynamics‐Processed Highly Stretchable, Conductive, and Printable Graphene Inks for Real‐Time Monitoring Sweat during Stretching Exercise

“…[23][24][25][26][27][28] They are widely used to print a variety of wearable electronics, transistors, sensors, solar cells, batteries, supercapacitors, and other devices [23,24,[29][30][31][32][33][34][35] The formulation of functional inks with unique properties is essential for printing wearable sensors. [36][37][38] Recently, 2D layered graphene materials have attracted considerable attention as promising conductive fillers for printed flexible and stretchable devices owing to their high electrical conductivity, excellent mechanical properties, and good chemical stability. [39][40][41][42] The successful preparation of solution-processed exfoliated graphene materials has accelerated the development of printable graphene inks for the low-cost and high-throughput manufacturing of flexible and wearable devices.…”

Droplet‐Based Techniques for Printing of Functional Inks for Flexible Physical Sensors

“…The second route is structural innovation through specially designed patterns such as in‐plane serpentine [ 196 ] and out‐of‐plane sinusoidal nanoribbons/nanomembranes [ 197 ] shapes that convert global strains to local buckling, bending, and twisting. [ 198 ] The former strategy endows superior degree of stretchability to electronics, however this is normally obtained with the cost of deteriorating the electrical performance. On the other side, structural innovation allows wider range of materials to be used for stretchable electronics, but often provides inferior stretchability.…”

Energy Autonomous Sweat‐Based Wearable Systems

“…The BFC obtained in this manner shows an OCP of 0.5 V, and a high‐power density of nearly 1.2 mW cm −2 at 0.2 V. The major advantages of interdigitated electrode design with serpentine interconnects for the circular anodic and cathodic electrode “islands” are: i) reduced internal resistance (hence decrease the power loss), ii) lower chances of electrodes short‐circuiting, and iii) high stretchability via uniform distribution of the stress. [ 77,191 ] In addition, the 3D porous structured cathodic and anodic electrode pellets enable high loading of active components. The power density of this BFC increased nearly linearly with increasing lactate concentration (Figure 5f) and the power density is ≈10 times than previously reported BFC.…”