Mechanical Properties of Organic Semiconductors for Stretchable, Highly Flexible, and Mechanically Robust Electronics

Abstract

Mechanical deformability underpins many of the advantages of organic semiconductors. The mechanical properties of these materials are, however, diverse, and the molecular characteristics that permit charge transport can render the materials stiff and brittle. This review is a comprehensive description of the molecular and morphological parameters that govern the mechanical properties of organic semiconductors. Particular attention is paid to ways in which mechanical deformability and electronic performance can coexist. The review begins with a discussion of flexible and stretchable devices of all types, and in particular the unique characteristics of organic semiconductors. It then discusses the mechanical properties most relevant to deformable devices. In particular, it describes how low modulus, good adhesion, and absolute extensibility prior to fracture enable robust performance, along with mechanical "imperceptibility" if worn on the skin. A description of techniques of metrology precedes a discussion of the mechanical properties of three classes of organic semiconductors: π-conjugated polymers, small molecules, and composites. The discussion of each class of materials focuses on molecular structure and how this structure (and postdeposition processing) influences the solid-state packing structure and thus the mechanical properties. The review concludes with applications of organic semiconductor devices in which every component is intrinsically stretchable or highly flexible.

Omnidirectional Strain‐Independent Organic Transistors Integrated onto an Elastomer Template with a Spontaneously Formed Fingerprint‐Mimicking Microtopography

“…yields estimated wavy structures with L ≈12.1, 36.4, and 91.0 µm for t = 200, 600, and 1500 nm, respectively, in the PD-flex template for the PMDS(1):Ecoflex(1) (Figure S4, Supporting Information). 2019,5, 1900441 Although the L value for the 1.5-µm-thick Parylene adlayer differs from the theoretically calculated value, the values for the other thicknesses are similar to the theoretical ones.…”

“…2019, 5,1900441 coated with the PD-flex was heated in a convection oven at 40 °C for 24 h to fully cure the elastomeric polymer. Electron.…”

“…[1][2][3][4] Such applications demand electronic devices with excellent mechanical flexibility, [5][6][7] good conformability, [8,9] ultralight weight, [10][11][12] and optical transparency under various types of external strain. [1][2][3][4] Such applications demand electronic devices with excellent mechanical flexibility, [5][6][7] good conformability, [8,9] ultralight weight, [10][11][12] and optical transparency under various types of external strain.…”

Optical Diffraction Strain Sensor Prepared by Interference Lithography

“…However, these methods cannot be applied in all cases and they require large size instruments. The measurement of deformation and monitoring of strain integrated with electronic elements are important in particular for systems such as flexible electronics [5][6][7], because in comparison to classical silicon electronics the stretchable elements are deformed to a larger degree. For such applications, the suitable method of strain measurement can be the use of light diffraction.…”

Charge-transport properties of 4-(1,2,2-triphenylvinyl)aniline salicylaldehyde hydrazone: tight-packing induced molecular `hardening'

“…Charge transport in organic materials is one of the most important properties in the performance of solar cells, organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), batteries and sensors (Root et al, 2017;Shirota & Kageyama, 2007;Wang et al, 2012). Since the 1950s, significant progress has been made towards improved understanding of intrinsic charge-transport phenomena in organic materials, and several models, such as the band model, the tight-binding model and the hopping model, have been proposed for the simulation and prediction of low-density intrinsic transport behaviour in organic crystals observed in OFET experiments (Grozema & Siebbeles, 2008;Shuai et al, 2011).…”