Controlling Film Formation and Host‐Guest Interactions to Enhance the Thermoelectric Properties of Nickel‐Nitrogen‐Based 2D Conjugated Coordination Polymers

Abstract

Two‐dimensional conjugated coordination polymers (cCPs) based on square‐planar transition metal‐complexes (such as MO4, M(NH)4, and MS4, M = metal) are an emerging class of (semi)conducting materials that are of great interest for applications in supercapacitors, catalysis, and thermoelectrics. Finding synthetic approaches to high‐performance nickel and nitrogen (Ni‐N) based cCP films has been a long‐standing challenge. Here, we develop a general, dynamically controlled on‐surface synthesis method that produces highly conductive Ni‐N‐based cCP thin films and study the thermoelectric properties as a function of the molecular structure and their dependence on interactions with the ambient atmosphere. Among the four studied cCPs with different ligand sizes hexaminobenzene‐ and hexaaminotriphenylene‐based films exhibit record electrical conductivity (100 – 200 S cm–1) in this Ni‐N based cCP family, which is one order of magnitude higher than previous reports, and the highest thermoelectric power factors up to 10 μW m–1 K–2 among reported 2D cCPs. We study the transport physics of these films and show that depending on the host‐guest interaction with oxygen/water the majority carrier type and the value of the Seebeck coefficient can be largely regulated. The high conductivity is likely reflecting good interconnectivity between (small) ordered domains with grain boundaries supporting disordered metallic transport.This article is protected by copyright. All rights reserved

Rational Construction of Two-Dimensional Conjugated Metal–Organic Frameworks (2D c-MOFs) for Electronics and Beyond

“…Even more captivating is the utilization of strategies to control the interlayer electronic coupling, which can balance the conductivity and Seebeck coefficient of 2D c-MOFs, thus tuning their thermoelectric performance . The measured Seebeck coefficients are 76.3 ± 2, 387.2 ± 2, and 423.8 ± 1 μV K –1 for Ni 3 (HATI_C1) 2 , Ni 3 (HATI_C3) 2 , and Ni 3 (HATI_C4) 2 , respectively.…”

Acid-Dependent Charge Transport in a Solution-Processed 2D Conductive Metal-Organic Framework

“…). − Previous studies have emphasized the importance of introducing electron-rich chelating motifs (–NH 2 , –SH) to organic linkers to enhance orbital overlaps between the metal cations and linkers. ,, There remains burgeoning interest in designing new tritopic linkers with dissimilar conjugated cores , and points to a central design principle: in-plane metal ligand covalency dictates bulk electrical conductivity. Thus, beyond substitution of metal and/or heteroatom, there is value in exploring other chemical handles that affects their interfacial chemistry …”

“…Thus, beyond substitution of metal and/or heteroatom, there is value in exploring other chemical handles that affects their interfacial chemistry. 22 In addition to their electrical properties, the facile processing of 2D MOFs into thin films is crucial for their application in electronic devices. 23 To achieve this, various fabrication techniques, including chemical vapor deposition, 24 layer-bylayer, 25 and microfluidic synthesis, 26 have been employed to craft high-quality thin films.…”