Recent advances in soft electronic materials for intrinsically stretchable optoelectronic systems

In recent years,significant progress has been achieved in the design and fabrication of stretchable optoelectronic devices.In general,stretchability has been achieved through geometrical modifications of device components,such as with serpentine interconnects or buckled substrates.However,the local stiffness of individual pixels and the limited pixel density of the array have impeded further advancements in stretchable optoelectronics.Therefore,intrinsically stretch-able optoelectronics have been proposed as an alternative approach.Herein,we review the recent advances in soft elec-tronic materials for application in intrinsically stretchable optoelectronic devices.First,we introduce various intrinsically stretchable electronic materials,comprised of electronic fillers,elastomers,and surfactants,and exemplify different in-trinsically stretchable conducting and semiconducting composites.We also describe the processing methods used to fabricate the electrodes,interconnections,charge transport layers,and optically active layers used in intrinsically stretch-able optoelectronic devices.Subsequently,we review representative examples of intrinsically stretchable optoelectronic devices,including light-emitting capacitors,light-emitting diodes,photodetectors,and photovoltaics.Finally,we briefly discuss intrinsically stretchable integrated optoelectronic systems.

Nanoscale Materials and Deformable Device Designs for Bioinspired and Biointegrated Electronics

Electronic devices whose structural and functional features are inspired by living creatures have unique performance and unconventional features that are not found in conventional electronic devices.In addition to such bioinspired electronics,with the rise of new fields such as personalized healthcare,mobile electronics,and big-data analysis,biointegrated electronic devices that can collect biomedical information from the human body through various biosensors and deliver appropriate therapeutic feedback stimulations in real time on the spot where immediate treatment is needed have become important.Because body parts and internal organs of living creatures,including humans,have curvilinear shapes and comprise mechanically soft tissues,such bioinspired and biointegrated electronic devices are required to match the soft and deformable features of biological tissues.Such soft and deformable features of electronic devices can be achieved by employing flexible and stretchable materials and unconventional device design techniques.These soft materials and deformable device designs dissipate stress originating from mechanical deformation of the device and thus retard crack generation and/or propagation in the device.Recently,technologies for nanoscale materials have shown a significant level of progress on their material performance and processing technologies.The nanoscale dimension of the electronic materials could achieve extremely small flexural rigidity in comparison to the bulk state of the same materials.Furthermore,techniques to form a well-percolated network of nanomaterials in the elastomeric matrix and to build a pathway for the facile electron and hole transport inside the polymer have induced dramatic performance advances of soft electronic materials,which led to nanocomposites that can accomplish both high mechanical deformability and high electrical performance at the same time.In addition,deformable device designs such as buckled structures and serpentine designs enhance the flexibility and stretchability of the device further.Because of their soft and deformable nature,bioinspired and biointegrated electronic devices could achieve device structures inspired by living creatures and make conformal contact to the target tissue for high-quality measurement of biological signals and real-time feedback treatments.Herein,we introduce recent advances in nanoscale materials and deformable device designs for bioinspired and biointegrated electronics.First,materials with various geometries(e.g.,one-dimensional(1D)nanowires and nanotubes,two-dimensional(2D)nanomembranes and nanoflakes,and three-dimensional(3D)networks of nanomaterials in polymers)are reviewed in terms of their deformable nature.Then,the representative device design strategies required for achieving a soft and deformable form factor(e.g.,buckling method,serpentine design,and kirigami technique)are reviewed.Examples of such state-of-the-art electronic devices are then presented,after which representative system-level applications,including electronic eyes,electronic skin,an electronic ear,wearable electronics,and implantable electronics,are described.Finally,we present a brief future outlook for the field of bioinspired and biointegrated electronics.