Thermoplastic Elastomer Tunes Phase Structure and Promotes Stretchability of High‐Efficiency Organic Solar Cells

Abstract

the power conversion efficiencies (PCEs) of OSCs show rapid increase and the values have increased to over 18%. [16][17][18][19][20][21][22][23][24] However, owing to the brittle nature of small molecules, [25] the mechanical properties of polymer:NF-SMA blends are generally insufficient and can hardly meet the requirement of stretchable electronics. [26,27] The mechanical imperceptibility of OSCs requires low stiffness and high extensibility for wearable and portable applications. The human skin exhibits a ductility of about 30%, which is the benchmark for skin-wearable devices. [28] Studies have been carried out to determine the mechanical properties of nonfullerene OSCs [29][30][31] and drive the development of stretchable OSCs. [32][33][34][35] For instance, the fracture strain of the well-known PTB7-Th:(3,9-bis(2-methylene-(3-(1,1dicyanomethylene)-indanone))-5,5,11,11tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene) (ITIC) blend films decreased dramatically with the increase of ITIC, and the blend films became significantly stiffer as a result of increased elastic modulus. [26,36] Therefore, methods should be adopted to improve the stretchability and reduce the stiffness of OSCs based on polymer:NF-SMA blends.As the mechanical performance of polymer:NF-SMA blends are often poor, a representative high-efficiency Top-performance organic solar cells (OSCs) consisting of conjugated polymer donors and nonfullerene small molecule acceptors (NF-SMAs) deliver rapid increases in efficiencies. Nevertheless, many of the polymer donors exhibit high stiffness and small molecule acceptors are very brittle, which limit their applications in wearable devices. Here, a simple and effective strategy is reported to improve the stretchability and reduce the stiffness of highefficiency polymer:NF-SMA blends and simultaneously maintain the high efficiency by incorporating a low-cost commercial thermoplastic elastomer, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS). The microstructure, mechanical properties, and photovoltaic performance of PM6:N3 with varied SEBS contents and the molecular weight dependence of SEBS on microstructure and mechanical properties are thoroughly characterized. This strategy for mechanical performance improvement exhibits excellent applicability in some other OSC blend systems, e.g., PBQx-TF:eC9-2Cl and PBDB-T:ITIC. More crucially, the elastic modulus of such complex ternary blends can be nicely predicted by a mechanical model. Therefore, incorporating thermoplastic elastomers is a widely applicable and cost-effective strategy to improve mechanical properties of nonfullerene OSCs and beyond.

Insulating Polymers as Additives to Bulk‐Heterojunction Organic Solar Cells: The Effect of Miscibility

“…Ye and coworkers comprehensively investigated the influence of SEBS (polystyrene-blockpoly(ethylene-ran-butylene)-block-polystyrene) in different BHJ blended systems. [13] They demonstrated that the incorporation of thermoplastic elastomers in the BHJ systems was a universal strategy to improve the stretchability, reduce the elastic modulus, and maintain the photovoltaic performance. Moreover, the changes in mechanical and photovoltaic properties have been ascribed to the morphology evolutions of the composite systems.…”

Eco‐friendly solution processing of all‐polymer solar cells: Recent advances and future perspective

“…Insertion of insulating breaking spacers (e.g., alkyls) to the backbones of conjugated polymers has been provided as a means to address the low ductility of Y6-based polymer acceptors. Besides, systematically characterizing the mechanical properties [104][105][106][107] of these polymer donors and acceptors might aid in the development of flexible and stretchable all-PSCs.…”

Morphology control in high‐efficiency all‐polymer solar cells

“…The film morphology of polymer blends not only affects the PCE of All-PSCs but also closely determines their mechanical property and stability. Revealing the fundamental connections between morphological parameters at different length scales and mechanical parameters 170,171 (elastic modulus, fracture energy, crack-onset strain, cohesion energy, toughness, and so on) warrants in-depth explorations. In future studies, a full set of polymer structure-morphology-property correlations should be further clarified to provide design rules for commercially viable novel All-PSCs.…”