Junhang Li,Chujun Zhang,Qiang Zhang,Sichun Wang,Rui Zhang,Zicheng Ding,Yanchun Han
Molecular weight optimization is crucial for high-performance stretchable conjugated polymer films. However, an in-depth understanding of molecular weight distribution on solution assembly, film microstructures, and electrical/mechanical properties of conjugated polymers is lacking. Herein, a model conjugated polymer, poly(indacenodithiophene-co-benzothiadiazole) (IDTBT), with a similar weight-average molecular weight but different polydispersity indexes (PDIs) of 3.2, 2.4, and 1.6 is investigated. The low-PDI polymer, containing a high content of homogeneous long chains, facilitates sufficient interchain aggregation caused by the enhanced chain entanglement and prolonged aggregation dynamics, which creates a low-crystallinity film containing long-chain well-connected aggregates and chain entanglement networks. Consequently, the charge mobility increases from 2.1 to 3.1 cm2 V–1 s–1 as PDI decreases from 3.2 to 1.6. During stretching, the polymer chains align more effectively along the strain direction in the low-PDI film, which creates more dynamic sliding sites and short-range aggregates to dissipate the strain energy. Thus, the low-PDI polymer film exhibits a high charge mobility of 1.0 ± 0.1 cm2 V–1 s–1 at 100% strain and 0.9 ± 0.1 cm2 V–1 s–1 after 100 cycles of stretching–releasing at 25% strain, which significantly outperforms the high-PDI film. This work demonstrates the significance of polydispersity optimization for developing mechanically robust polymer semiconductor films in stretchable electronics.
A continuous network with short-range aggregation structures in an amorphous matrix is widely recognized for achieving optimal electronic and mechanical performance of conjugated polymer films. The size and structural order of these aggregates critically determine the ability to accommodate and dissipate strain without disrupting the charge transport pathways. Here, we systematically investigated the effect of polymer chain dynamics on the evolution of aggregation structure for the conjugated polymer poly(indacenodithiophene-co-benzothiadiazole) (IDTBT) by controlling the annealing temperature (Ta). In the as-cast film, the polymer backbone remains kinetically trapped in a distorted conformation, leading to a loosely packed and disordered morphology. Thermal annealing at 100 °C, between the backbone glass transition temperatures (Tg) and the disaggregation temperature (Tdisagg), activates the segment motion, enabling reorganization into small, short-range ordered aggregates with an extended conformation. When annealed at 260 °C (Ta > Tdisagg), full chain mobility permits assembly into larger, more ordered aggregates with dense molecular packing. Consequently, the charge mobility increases from 0.92 cm2 V–1 s–1 in the as-cast film to 3.14 cm2 V–1 s–1 after annealing at 260 °C. Under strain, the film annealed at 100 °C retains its short-range aggregates, which facilitates efficient stress dissipation through interlayer slip and preserves charge mobility. In contrast, the film annealed at 260 °C exhibits premature fracture of the large ordered aggregates accompanied by restricted chain alignment. As a result, the film annealed at 100 °C maintains a charge mobility of 0.86 cm2 V–1 s–1 under 100% strain, whereas the 260 °C-annealed film exhibits a substantially lower mobility of 0.14 cm2 V–1 s–1. These results underscore the critical role of short-range aggregation structures in achieving high-performance stretchable conjugated polymer films.
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