This Minireview compares two distinct ink types, namely metal-organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low-cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solutionbased processes that historically have employed NP formula-tions to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks.

Bidentate diamine and amino‐alcohol ligands have been used to form solid, water‐soluble, and air‐stable monomeric copper complexes of the type [Cu(NH2CH2CH(R)Y)2(NO3)2] (1, R=H, Y=NH2; 2, R=H, Y=OH; 3, R=Me, Y=OH). The complexes were characterized by elemental analysis, mass spectrometry, infrared spectroscopy, thermal gravimetric analysis, and single‐crystal X‐ray diffraction. Irrespective of their decomposition temperature, precursors 1–3 yield highly conductive copper features [1.5×10−6 Ω m (±5×10−7 Ω m)] upon atmospheric‐pressure plasma‐enhanced sintering.

Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low‐cost flexible substrates, materials for wearable devices and beyond. Although nanoparticle (NP) inks are well known, the rise in metal‐organic decomposition (MOD) inks has extended the range of compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. For more information, see the Minireview by C. E. Knapp et al. on page 8062 ff.

The field of printed electronics strives for lower processing temperatures to move toward flexible substrates that have vast potential: from wearable medical devices to animal tagging. Typically, ink formulations are optimized using mass screening and elimination of failures; as such, there are no comprehensive studies on the fundamental chemistry at play. Herein, findings which describe the steric link to decomposition profile: combining density functional theory, crystallography, thermal decomposition, mass spectrometry, and inkjet printing, are reported. Through the reaction of copper(II) formate with excess alkanolamines of varying steric bulk, tris-co-ordinated copper precursor ions: "[CuL 3 ]," each with a formate counter-ion (1-3) are isolated and their thermal decomposition mass spectrometry profiles are collected to assess their suitability for use in inks (I 1-3 ). Spin coating and inkjet printing of I 1,2 provides an easily up-scalable method toward the deposition of highly conductive copper device interconnects (𝝆 = 4.7-5.3 × 10 −7 𝛀 m; ≈30% bulk) onto paper and polyimide substrates and forms functioning circuits that can power light-emitting diodes. The connection among ligand bulk, coordination number, and improved decomposition profile supports fundamental understanding which will direct future design.

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