Presynthetic Redox Gated Metal-to-Insulator Transition and Photothermoelectric Properties in Nickel Tetrathiafulvalene-Tetrathiolate Coordination Polymers

Abstract

Photothermoelectric (PTE) materials are promising candidates for solar energy harvesting and photodetection applications, especially for near-infrared (NIR) wavelengths. Although the processability and tunability of organic materials are highly advantageous, examples of organic PTE materials are comparatively rare and their PTE performance is typically limited by poor photothermal (PT) conversion. Here, we report the use of redox-active Sn complexes of tetrathiafulvalene-tetrathiolate (TTFtt) as transmetalating agents for the synthesis of presynthetically redox tuned NiTTFtt materials. Unlike the neutral material NiTTFtt, which exhibits n-type glassy-metallic conductivity, the reduced materials Li1.2Ni0.4[NiTTFtt] and [Li­(THF)1.5]1.2Ni0.4[NiTTFtt] (THF = tetrahydrofuran) display physical characteristics more consistent with p-type semiconductors. The broad spectral absorption and electrically conducting nature of these TTFtt-based materials enable highly efficient NIR-thermal conversion and good PTE performance. Furthermore, in contrast to conventional PTE composites, these NiTTFtt coordination polymers are notable as single-component PTE materials. The presynthetically tuned metal-to-insulator transition in these NiTTFtt systems directly modulates their PT and PTE properties.

Broad Electronic Modulation of Two-Dimensional Metal–Organic Frameworks over Four Distinct Redox States

“…The dominant p-type character in Fe 4 (THT) 2 , Li 3 Fe 3 (THT) 2 , and Li 2 Fe 3 (THT) 2 may originate from the Fe­(III) centers acting as acceptors as proposed in other Fe-based MOFs. , The transition to n-type behavior on oxidation may therefore be ascribed to the generation of unpaired ligand-based electrons as donors and ultimately change the dominant carrier type in the system. We note that most 2D semiconductors are n-type due to electron doping from interfacial charge impurities and defects; the search for p-type 2D semiconductors as well as p–n switchable materials is of great interest . Here, we demonstrate synthetic tuning to realize p-type 2D semiconductors as well as p–n switching via redox manipulations.…”

Tetrathiafulvalene-2,3,6,7-tetrathiolate linker redox-state elucidation via S K-edge X-ray absorption spectroscopy

“…Direct correlation between spectroscopic evidence and TTFtt oxidation state is lacking despite observed differences in vibrational, UV-visible, and near-infrared data between TTFtt redox isomers. 13 X-ray absorption spectroscopy (XAS) enables experimental examination of oxidation states and covalency. In particular, S K-edge XAS enables analysis of the redox states of non-innocent S-based ligands in dithiolene compounds.…”

Significantly Boosted Photothermoelectric Effect via Carrier Injection in Au Decorated SWCNT Films for Infrared Detection

“…Comparison on output voltage values of photodetectors made from various material systems based on PTE effect with respect to power density between this work and the literature. [ 8,16–21,23–43 ] …”