Development of Thiophene Based Conjugated Polymers in Two Dimensions

Project Information

T2DCP

Grant agreement ID: 819698

DOI

10.3030/819698

Project closed

EC signature date 6 February 2019

Start date 1 March 2019

End date 31 August 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 000 000,00

EU contribution

€ 2 000 000,00

Coordinated by

TECHNISCHE UNIVERSITAET DRESDEN
Germany

Periodic Reporting for period 4 - T2DCP (Development of Thiophene Based Conjugated Polymers in Two Dimensions)

Reporting period: 2023-09-01 to 2024-08-31

Summary of the context and overall objectives of the project

1. What are the problems?
Linear conjugated polymers (CPs) are excellent organic semiconductors. But hopping between adjacent polymer chains limits the delocalization of charge carriers, resulting in insufficient charge carrier mobility. The development of two-dimensional (2D) CPs can establish multiple charge transport strands to facilitate transport. Despite the growing interest in developing 2D polyimines and phenylene-based 2D CPs, they typically suffer from poor π-electron delocalization with intrinsic charge mobilities typically below 1 cm2 V−1 s−1. Meanwhile, the reported synthetic methodologies employ the bottom-up methods, which lacks of precise control on the reaction kinetics and normally results in 2D CPs with poor crystallinity with domain size <100 nm, presenting difficulties in reaching their full potential in electronics.

2. Why is this important for society?
Improving charge transport is critical for developing the next generation of electronics, from faster and more efficient transistors to advanced energy devices. Society is increasingly reliant on high-performance electronic materials for technologies such as smartphones, renewable energy systems, and medical devices. Addressing these limitations can lead to breakthroughs in energy efficiency, sustainability, and device performance, benefiting industries and consumers alike.

3. What are the overall objectives?
In this project, we aim for the development of a series of novel solution-synthesis methods towards highly crystalline 2D CPs. One core objective is to pioneer interface-assisted synthesis methodologies and synthetic chemistry for the precision synthesis of novel 2D CPs. To enhance the 2D conjugation for high charge mobility, we aim to incorporate the highly planar thiophene units into the 2D poly(arylene vinylene) (2D PAV) backbones. The development of donor-acceptor-type 2D PAVs would strengthen the dispersion of conduction bands for electron transport. To further increase the effective π-conjugation length, we aim to construct 2D poly(benzimidazobenzophenanthroline)s (2D BBLs). We also aim to explore the applications of 2D CPs in van der Waals heterostructures (vdWhs) and multifunctional electronic devices. In addition, we will integrate highly crystalline 2D CPs into electronic and energy devices to achieve excellent performance that outperforms the state-of-the-art.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In this project, we first focused on developing novel linkage chemistry for constructing crystalline 2D PAVs with crystalline domain sizes up to 100 nm, such as Horner-Wadsworth-Emmons (HWE) and Wittig 2D polycondensations, Knoevenagel 2D polycondensation combined with Michael-addition-elimination.

Based on the established methods, we synthesized the first fully thiophene-based 2D PAVs from a thienyl-benzodithiophene (TBDT) monomer, which presents a high charge mobility at room temperature. We further demonstrated the first crystalline 2D BBLs, which shows band transport behavior and the state-of-the-art charge mobility among polymer semiconductors. Further advancements include the development of several types of curved graphene nanoribbons bearing cove regions. The chemical and crystal structures, thermal and chemical stabilities, and band gaps of the developed materials were thoroughly characterized.

In 2019, we developed a surfactant-monolayer-assisted interfacial synthesis (SMAIS) method to guide the preorganization and 2D polymerization of rigid monomers on the water surface. This method allowed the synthesis of few-layer 2D polymers with high crystallinity. The assembly and 2D polymerization processes were monitored in real-time. This approach was extended to a range of linkage chemistries, such as dynamic covalent Schiff-base and Knoevenagel reactions as well as kinetically irreversible Katritzky reactions. The resulting thin films were free-standing with large areas, preferential layer orientation, tunable thickness and crystal domains up to 120 μm².

Based on the thin-film samples, we studied the proximity effect of 2D CPs via fabricating vdWHs. Vertically stacking monolayer 2D CPs with other 2D materials, such as graphene and MoS2, showcased efficient interlayer charge transfer through various spectroscopies, highlighting the immense potential of 2D CP-based vdWHs in exploring interfacial physical phenomena. In the end, the applications of 2D CPs were also demonstrated in hybrid memory devices, osmotic power generators, organic light-emitting diodes, thermoelectrics, chemiresistors, catalysis, electrochromic devices, and energy storage devices.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Regarding to synthetic linkage chemistry, we have developed a series of novel synthetic methodologies including HWE/Wittig 2D polycondensation, Michael-addition-elimination-assisted Knoevenagel 2D polycondensation, and so on. The obtained 2D PAVs show crystalline domain sizes up to 100 nm beyond the state-of-the-art.

The developed SMAIS method represents a groundbreaking approach in guiding the 2D polymerization of rigid monomers on the water surface, enabling the synthesis of highly crystalline 2D CPs, a step beyond conventional solution method. On the other hand, this synthesis approach allows for precise thickness control, ranging from monolayer to few layers, and up-scalable preparation of 2D CP films, which has not been fully realized in the previous methodologies.

Using the SMAIS method, we have synthesized many unprecedented few-layer 2D CPs on the water surface, for example, 2D polyimide, 2D polyamide, 2D polyimine, quasi 2D polyaniline and 2D polypyrrole, and so on. The crystal structure of 2D CPs and the defect sites have been resolved at the molecular level.

Regarding to electronic properties of 2D CPs, combining multiscale dc and ac measurements and theoretical calculation, we have established reliable structure-electronic property relationships in this type of materials. We demonstrated the first example of fully thiophene-based 2D PAV and 2D BBLs, which have presented optical band gaps as narrow as 1.3 eV. The 2D BBLs shows a unique band transport behavior with a high charge mobility of 970 cm2V1s1 at room temperature, which represents a record among the reported polymer semiconductors.

Moving to function, we integrated free-standing 2D polymer films into organic thin film/Si nanowire-based FETs to mimic neuronal synapses. Charged 2D CP single crystals were used as an anion-selective membrane for osmotic energy generation, superior to graphene and boron nitride. Moreover, 2D PAV films were utilized for coating the graphite cathode in batteries, enabling improvement of capacity and cycling life.

In 2021, we reported the preparation of 2D polyimide-graphene vdWhs, which showed an interlayer charge transfer time of about 60 fs comparable to that of the fastest inorganic vdWHs. Moreover, 2D polyimide/MoS2 vdWH exhibits strong interlayer coupling, significant charge transfer, and remarkably high electron mobility, exceeding that of pristine MoS2.