Branched Polyethylene as a Plasticizing Additive to Modulate the Mechanical Properties of π-Conjugated Polymers

Abstract

A new approach for improving the mechanical properties of semiconducting polymers was established via physical combination of a diketopyrrolopyrrole-based conjugated polymer with a low-molecularweight branched polyethylene (BPE). The influence of the BPE additive on the stretchability and mechanical properties of the conjugated polymer was studied at different scales, using various characterization techniques, including atomic force microscopy, UV−vis spectroscopy, and grazing incidence X-ray diffraction. At the micron scale, the BPE additive acts as a plasticizer and significantly reduces Young's modulus of the conjugated polymer and increases the crack onset strain, reaching a maximum of a 75% strain elongation when 90 wt % of BPE is blended with the conjugated polymer. The introduction of BPE to the blended systems decreases the crack propagation of polymer thin films, making them softer and more ductile, with Young's modulus of 112 MPa at 25 wt % of BPE before thermal annealing. At the nanoscale, the improvement of stretchability is shown by the reduction of the crack size under a 100% strain, going from 3100 to 600 nm at 0 and 90 wt % of BPE, respectively. The results obtained in this investigation confirm that an improvement in the mechanical properties and a modulation of the solid-state morphology of the semiconducting materials can be enabled by the physical mixing of conjugated polymers with a nontoxic, low-molecular-weight branched polyethylene, particularly favorable for the solution deposition of organic semiconductors.

From Chlorinated Solvents to Branched Polyethylene: Solvent‐Induced Phase Separation for the Greener Processing of Semiconducting Polymers

“…[21,22] Notably, previous studies of BPE in organic electronics showed that utilization of BPE as an additive for the solution processing of semiconducting polymers can significantly impact the optoelectronic and thermomechanical properties of semiconducting polymers. [23,24] However, in these previous examples, processing of the semiconducting polymers with toxic chlorinated solvent was critical and still required. While the amount of chlorinated solvents is negligible when spincoating is used for processing, solutions prepared from as low as 2 wt% of chlorinated solvents can be significantly challenging to use at large-scale due to toxicity and high boiling point.…”

Water‐assisted mechanical testing of polymeric thin‐films

“…(Figure 8(A)) Thus, it is vital to establish the structure‐thermal/mechanical property relationship of semiconducting polymer thin films for the design of next‐generation stretchable CPs. In the past decade, two primary strategies have been applied to tune the mechanical response of CPs: molecular engineering, including regioregularity, molecular weight, and backbone/side‐chain engineering; as well as postmodification, including cross‐linking, physical blending, and etc 20,69,119,120,124–132 . In this section, we briefly summarized the past efforts along this line to highlight the scientific significance of water‐assisted tensile tests.…”

“…In the past decade, two primary strategies have been applied to tune the mechanical response of CPs: molecular engineering, including regioregularity, molecular weight, and backbone/side-chain engineering; as well as postmodification, including cross-linking, physical blending, and etc. 20,69,119,120,[124][125][126][127][128][129][130][131][132] In this section, we briefly summarized the past efforts along this line to highlight the scientific significance of water-assisted tensile tests. The mechanical property of representative semiconducting polymers was also listed in Table 1.…”

Versatile methods for improving the mechanical properties of fullerene and non-fullerene bulk heterojunction layers to enable stretchable organic solar cells

“…In a second approach, we utilize a physical blending approach whereby an elastomer is composited with the BHJ as an effective approach to mechanically soften the photoactive layer. 27,29,30,36,37 For the first time to our knowledge, we successfully implement elastomers as plasticizer components into photoactive BHJ layer of OPV devices. Unlike bis-azide molecules, which covalently bond to two PC 61 BM molecules, requires chemical specificity and treatment such as thermal annealing, the elastomer does not covalently bond with any BHJ component.…”