Improving Electrical and Mechanical Properties of Blend Films Via Optimizing Solution-Processable Techniques and Controlling the Semiconductor Molecular Weight

Blending semiconductor polymers (SPs) with insulator polymers (IPs) is an effective strategy for preparing high-performance stretchable electronics. The key is the continuity of the semiconductor structure in the blend films, so the precise regulation of phase separation is the major challenge. Here, two key strategies that influence blend films were systematically investigated, including optimizing the solution-processable technique and controlling the semiconductor molecular weight (labeled LSP for 23.5 kDa, MSP for 108.5 kDa, and HSP for 222.6 kDa). Compared to the spin-coated (SC) films, the assembly on water-surface (AOW) films have uniform morphology, ordered microstructure, and better charge transport properties. During the formation of AOW films, SPs and IPs tend to move toward air and water, respectively, yielding a vertical phase separation structure. Moreover, a proportion of SPs are embedded in the SEBS matrix, with LSP forming an aggregated island structure and HSP forming a nanobunch network structure. For LSP, the introduction of an appropriate amount of SEBS can assist in the formation of an ordered film microstructure. The average mobility of the blend film LSP-SEBS (30%) is around 2.52 cm2 V–1 S–1, much higher than that of the neat film LSP (1.03 cm2 V–1 S–1). For HSP, the mechanical properties can be significantly improved by tuning the amount of SEBS, while maintaining favorable electrical properties. The highest mobility at 100% strain was calculated to be 0.73 and 0.21 cm2 V–1 S–1, for the blend film HSP-SEBS (70%) and the neat film HSP, respectively. Therefore, this study shows that optimizing the solution-processable technique as well as controlling the semiconductor molecular weight are promising and effective strategies for developing blend films, with good electrical and mechanical properties

Side Chain Engineering: Achieving Stretch-Induced Molecular Orientation and Enhanced Mobility in Polymer Semiconductors

Polymer semiconductors have been widely studied as an important component of stretchable electronic devices. However, most stretchable polymer semiconductors suffer from different degrees of charge mobility degradation at high strain. Here, we report a novel side chain engineering strategy to realize stretch-induced enhancement of molecular orientation and charge transport in donor–acceptor conjugated polymers. Specifically, hybrid siloxane-based side chains wifth different silicon chain lengths were grafted onto a backbone of poly-diketo-pyrrolopyrrole-selenophene (PTDPPSe). The charge mobility can be enhanced with an appropriate increase of the silicon chain length. Most importantly, increasing the silicon chain length resulted in significant improvement of stretchability, including decreasing elastic modulus and increasing fracture strain. Interestingly, charge mobilities parallel to the stretching direction for PTDPPSe-4Si, PTDPPSe-5Si, and PTDPPSe-6Si are all above 1 cm2 V–1 s–1 at 100% strain, higher than those of their unstretched states. This enhanced charge mobility is attributed to the excellent ductility and high strain-induced alignment of polymer chains. The current study is expected to provide guidance for the design of intrinsically stretchable polymer semiconductors and advance the development of wearable electronics