Facile Approach to Fabricating Stretchable Organic Transistors with Laser-Patterned Ag Nanowire Electrodes

Intrinsically Stretchable Polymer Semiconductors with Good Ductility and High Charge Mobility through Reducing the Central Symmetry of the Conjugated Backbone Units

Intrinsically stretchable polymer semiconductors are highly demanding for flexible electronics. However, it still remains challenging to achieve synergy between intrinsic stretchability and charge transport property properly for polymer semiconductors. In this paper, terpolymers are reported as intrinsically stretchable polymeric semiconductors with good ductility and high charge mobility simultaneously by incorporation of non-centrosymmetric spiro[cycloalkane-1,9'-fluorene] (spiro-fluorene) units into the backbone of diketopyrrolopyrrole (DPP) based conjugated polymers. The results reveal that these terpolymers show obviously high crack onset strains and their tensile moduli are remarkably reduced, by comparing with the parent DPP-based conjugated polymer without spiro-fluorene units. They exhibit simultaneously high charge mobilities (>1.0 cm² V^-1 s^-1 ) at 100% strain and even after repeated stretching and releasing cycles for 500 times under 50% strain. The terpolymer P2, in which cyclopropane is linked to the spiro-fluorene unit, is among the best reported intrinsically stretchable polymer semiconductors with record mobility up to 3.1 cm² V^-1 s^-1 at even 150% strain and 1.4 cm² V^-1 s^-1 after repeated stretching and releasing cycles for 1000 times.

Stretchable conductors for stretchable field-effect transistors and functional circuits

Stretchable electronics have received intense attention due to their broad application prospects in many areas, and can withstand large deformations and form close contact with curved surfaces. Stretchable conductors are vital components of stretchable electronic devices used in wearables, soft robots, and human-machine interactions. Recent advances in stretchable conductors have motivated basic scientific and technological research efforts. Here, we outline and analyse the development of stretchable conductors in transistors and circuits, and examine advances in materials, device engineering, and preparation technologies. We divide the existing approaches to constructing stretchable transistors with stretchable conductors into the following two types: geometric engineering and intrinsic stretchability engineering. Finally, we consider the challenges and outlook in this field for delivering stretchable electronics.

Highly-integrated, miniaturized, stretchable electronic systems based on stacked multilayer network materials

Elastic stretchability and function density represent two key figures of merits for stretchable inorganic electronics. Various design strategies have been reported to provide both high levels of stretchability and function density, but the function densities are mostly below 80%. While the stacked device layout can overcome this limitation, the soft elastomers used in previous studies could highly restrict the deformation of stretchable interconnects. Here, we introduce stacked multilayer network materials as a general platform to incorporate individual components and stretchable interconnects, without posing any essential constraint to their deformations. Quantitative analyses show a substantial enhancement (e.g., by ~7.5 times) of elastic stretchability of serpentine interconnects as compared to that based on stacked soft elastomers. The proposed strategy allows demonstration of a miniaturized electronic system (11 mm by 10 mm), with a moderate elastic stretchability (~20%) and an unprecedented areal coverage (~110%), which can serve as compass display, somatosensory mouse, and physiological-signal monitor.

Patterning of Metal Nanowire Networks: Methods and Applications

With the advance in flexible and stretchable electronics, one-dimensional nanomaterials such as metal nanowires have drawn much attention in the past 10 years or so. Metal nanowires, especially silver nanowires, have been recognized as promising candidate materials for flexible and stretchable electronics. Owing to their high electrical conductivity and high aspect ratio, metal nanowires can form electrical percolation networks, maintaining high electrical conductivity under deformation (e.g., bending and stretching). Apart from coating metal nanowires for making large-area transparent conductive films, many applications require patterned metal nanowires as electrodes and interconnects. Precise patterning of metal nanowire networks is crucial to achieve high device performances. Therefore, a high-resolution, designable, and scalable patterning of metal nanowire networks is important but remains a critical challenge for fabricating high-performance electronic devices. This review summarizes recent advances in patterning of metal nanowire networks, using subtractive methods, additive methods of nanowire dispersions, and printing methods. Representative device applications of the patterned metal nanowire networks are presented. Finally, challenges and important directions in the area of the patterning of metal nanowire networks for device applications are discussed.

Dynamic Mechanical Analysis of Polymer Thin Films Using a Kirigami-Inspired Support

A method of determining the mechanical relaxation behavior of polymer thin films is presented that employs a kirigami-inspired sample support. The film of interest is placed on the kirigami support and loaded into a dynamic mechanical analyzer. When the composite is placed in tension, the substrate effectively transfers the load to the film of interest. We demonstrate the approach using a number of polymers and conjugated polymer: small molecule blends relevant for organic photovoltaics. The kirigami-inspired method is found to provide an accurate view of thermal relaxation behavior in polymer thin films, including a quantitative assessment of the film storage modulus. The method is particularly valuable in thin films where film morphology is highly dependent on processing conditions. We show that differences in casting conditions have a clear impact on the thermal relaxation of both the neat and blend conjugated polymer films.

High-Performance Flexible Transparent Electrodes Fabricated via Laser Nano-Welding of Silver Nanowires

Silver nanowires (Ag-NWs), which possess a high aspect ratio with superior electrical conductivity and transmittance, show great promise as flexible transparent electrodes (FTEs) for future electronics. Unfortunately, the fabrication of Ag-NW conductive networks with low conductivity and high transmittance is a major challenge due to the ohmic contact resistance between Ag-NWs. Here we report a facile method of fabricating high-performance Ag-NW electrodes on flexible substrates. A 532 nm nanosecond pulsed laser is employed to nano-weld the Ag-NW junctions through the energy confinement caused by localized surface plasmon resonance, reducing the sheet resistance and connecting the junctions with the substrate. Additionally, the thermal effect of the pulsed laser on organic substrates can be ignored due to the low energy input and high transparency of the substrate. The fabricated FTEs demonstrate a high transmittance (up to 85.9%) in the visible band, a low sheet resistance of 11.3 Ω/sq, high flexibility and strong durability. The applications of FTEs to 2D materials and LEDs are also explored. The present work points toward a promising new method for fabricating high-performance FTEs for future wearable electronic and optoelectronic devices.