Hio-Ieng Un1
University of Cambridge1
Two-dimensionally (2D) conjugated metal-organic frameworks that represent an emerging class of materials with rich chemistry and physics have shown great potential in electrochemical, optoelectronic, and catalytic applications. These 2D conducting MOFs can be synthesied in a “solution-processed” mild manner. However, unlike organic semiconductors in which microstructure and ordering can be reconstructed during fabrication, 2D conducting MOFs are neither soluble nor meltable at general conductions once made. Therefore, precise (chemical and positional) structural control in solid state during synthesis at various length scales are of particular importance.<br/>In the first part, we will present a general on-surface synthesis method towards highly conductive thin films of nitrogen-coordinated 2D conducting MOFs. The universality of this method is demonstrated with fours materials systems with different pore sizes and different carrier types (hole and electron). Two of them exhibit record electrical conductivity (100 – 200 S cm<sup>-1</sup>) and power factor (5 uW m<sup>-1</sup> K<sup>-2</sup>) for this nitrogen-coordinated MOF family. Their electronic and thermoelectric stabilities are also investigated. The universal method reported here provides access to understanding the fundamentals and potential in applications.<br/>In the second part, we will focus on the interplay between (chemical and micro) structure, defects, and charge and thermoelectric transports. A range of sulfur-coordinated material systems with different chemical compositions are synthesied through liquid-liquid interfacial method. Unexpectedly, these MOFs exhibit irregular nano- and micro-architecture. The origin and the nature of the chemical defects and their vertical distributions will be discussed. Such chemical defects further lead to structural (positional) disorder. Notably, however, no evidence indicates that these defects may hinder electronic delocalization, which is different from many organic and inorganic (semi)conductors. Lastly, a possible transport mechanism for these 2D conducting MOFs will be discussed.