Increasing the Strength, Hardness, and Survivability of Semiconducting Polymers by Crosslinking

Abstract

Crosslinking is a ubiquitous strategy in polymer engineering to increase the thermomechanical robustness of solid polymers but has been relatively unexplored in the context of π‐conjugated (semiconducting) polymers. Notwithstanding, mechanical stability is key to many envisioned applications of organic electronic devices. For example, the wide‐scale distribution of photovoltaic devices incorporating conjugated polymers may depend on integration with substrates subject to mechanical insult—for example, road surfaces, flooring tiles, and vehicle paint. Here, a four‐armed azide‐based crosslinker (“4Bx”) is used to modify the mechanical properties of a library of semiconducting polymers. Three polymers used in bulk heterojunction solar cells (donors J51 and PTB7‐Th, and acceptor N2200) are selected for detailed investigation. In doing so, it is shown that low loadings of 4Bx can be used to increase the strength (up to 30%), toughness (up to 75%), hardness (up to 25%), and cohesion of crosslinked films. Likewise, crosslinked films show greater physical stability in comparison to non‐crosslinked counterparts (20% vs 90% volume lost after sonication). Finally, the locked‐in morphologies and increased mechanical robustness enable crosslinked solar cells to have greater survivability to four degradation tests: abrasion (using a sponge), direct exposure to chloroform, thermal aging, and accelerated degradation (heat, moisture, and oxygen).

Structural Insights into Conjugated Polymers for Stretchable Organic Transistors

“…101,102 Additionally, there have been instances where low MW polymers were employed to enhance mechanical robustness. 37 As shown in Figure 7e, the crystallite alignment was confirmed via macroscopically cross-polarized images of four types of cross-linkers with different crystallinities (crystallinity order: linear-H > linear > branch-H and branch, where H denotes hydrogen bonding for self-assembly). These four newly synthesized perfluoro phenyl azide alkyl crosslinkers with different numbers of branching and H-bonding units were introduced into the DPP-based copolymer, DPP-10C 5 DE.…”

“…Characterizing CP films using conventional mechanical testing methods such as the universal tensile test and Izod impactstrength test is challenging owing to their thinness. 34,35 Over the past few decades, a few methods to investigate the mechanical properties of nanometer-thick films have been developed, such as compressive nanoindentation, 36,37 doublecantilever beam, 38,39 flexural bending measurement, 40 and dynamic mechanical analysis. 41−44 Among them, the uniaxial tensile testing method, a representative mechanical evaluation tool, is highlighted to narrow the scope of this review.…”

Tailoring Molecular‐Scale Contact at the Perovskite/Polymeric Hole‐Transporting Material Interface for Efficient Solar Cells

“…To further understand the adhesion at perovskite/PTAA interface, 90°peel tests were performed on ITO/SnO 2 /perovskite/ PTAA thin films with or without 4TeI treatment (Figure 3bd). [27,[33][34][35] Delamination failure occurred at the weakest interface, which was the perovskite/PTAA interface for both 4TeI-treated and control samples (Figure S17, Supporting Information). However, with 4TeI surface treatment, the average peeling strength increased more than two-fold when compared with the control (without ligand passivation), from 32.6 to 69.5 N m −1 .…”

Covalent Topochemical Photo-Cross-Linking of Diketopyrrolopyrrole-Based Polymers with Polydiacetylenes toward Tunable Mechanical and Electronic Properties

“…Organic semiconductors, particularly π-conjugated polymers, are especially promising electroactive materials for designing printable, sustainable, and mechanically compliant technologies. − With an ever-increasing number of design strategies for organic materials to achieve electronic performance comparable to that of amorphous silicon, scientists now have access to a materials toolbox for creating organic electronics with unique properties. , In recent years, conjugated semiconducting polymers have been successfully integrated into a wide range of thin film electronics, including organic field-effect transistors (OFETs), organic light-emitting diodes, large-area organic photovoltaics, and others. − Among the various unique properties of semiconducting polymers, their tunable mechanical properties in thin films are particularly advantageous for applications such as smart coatings and skin-inspired electronics. − For this reason, a myriad of novel polymer designs has been reported utilizing various synthetic and processing strategies to control the thermomechanical properties of these materials, including the incorporation of chemical motifs capable of forming noncovalent interactions within the backbone and side chains of the polymers, the manipulation of material regioregularity, and the introduction of plasticizing additives and fillers. − …”