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Controlled insulator-to-metal transformation in printable polymer composites with nanometal clusters

Abstract

Although organic semiconductors have received the most attention, the development of compatible passive elements, such as interconnects and electrodes, is also central to plastic electronics. For this, ligand-protected metal-cluster films have been shown to anneal at low temperatures below 250C to highly conductive metal films, but they suffer from cracking and inadequate substrate adhesion. Here, we report printable metal-cluster–polymer nanocomposites that anneal to a controlled-percolation nanostructure without complete sintering of the metal clusters. This overcomes the previous challenges while still retaining the desired low transformation temperatures. Highly water- and alcohol-soluble gold clusters (75 mg ml−1) were synthesized and homogeneously dispersed into poly(3,4-ethylenedioxythiophene) to give a material with annealed d.c. conductivity tuneable between 10−4 and 105 S cm−1. These composites can inject holes efficiently into all-printed polymer organic transistors. The insulator–metal transformation can also be electrically induced at 1 MV cm−1, suggesting possible memory applications.

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Figure 1: Highly water- and alcohol-soluble nanogold dispersions.
Figure 2: Film d.c. conductivity as a function of anneal temperature (hotplate: ramp rate 2C min−1) in nitrogen.
Figure 3: Surface morphology of nanogold films with and without the polymer matrix.
Figure 4: Thermally induced insulator-to-metal transformation.
Figure 5: All-printed polymer FET.
Figure 6: Electrically induced insulator-to-metal transformation.

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Acknowledgements

We thank NUS (Project 144-000-131-112) and A*STAR (Project 052-117-0030) for funding.

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Correspondence to Lay-Lay Chua or Peter K.-H. Ho.

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The authors declare no competing financial interests.

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Supplementary information I, II and II; figures S1 and S2; tables S1 and S2 (PDF 581 kb)

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Sivaramakrishnan, S., Chia, PJ., Yeo, YC. et al. Controlled insulator-to-metal transformation in printable polymer composites with nanometal clusters. Nature Mater 6, 149–155 (2007). https://doi.org/10.1038/nmat1806

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