Conductivity in Thin-Films of Transition Metal Coordination Complexes

Abstract

In electronic commercial devices silicon remains the dominant material. Although it shows many advantages it requires usually high energy demand processes. Moreover, modifications of the electronic and physical properties are usually coupled with those processes.[ 1 ] While organic semiconductors usually show low energy processes and deposition with the desirable tunability reached with well-established synthesises.[ 2 ] Coordination complexes can even have an easier way of tunability by simply change the metal cores involved in the formation of the compounds. We aimed to design two coordination compounds formed by two complexes with equal but opposite charge and checking how the conductivity changes upon the metal substitution. They were synthetised by metathesis reaction by combining dithiolene complexes [M(mnt)2]2- (mnt = maleonitriledithiolate) M = Ni2+, Cu2+ with a copper coordination complexes [Cu(Stetra)]2+ (Stetra = 6,6’-bis(4,5-dihydrothiazol-2-yl)-2,2’-bipyridine). Upon the substitution of the metal core the system passed from insulator (Ni) to semiconductor behaviour (Cu) with a value of 10-8 (S/cm) and an activation energy of 0.9 eV. Their properties were investigated by using UV-Vis absorption, cyclic voltammetry, Raman spectroscopy, powder XRD, and conductivity. UV-Vis absorption and cyclic voltammetry were performed, in solid state, for the approximation of the energy levels. To support our investigations and experimental results computational modelling was performed. It revealed the central role that the copper has upon the conductivity compared to nickel. The lower reorganisation energy showed by the copper complex Cu(mnt)2 2- in solid state results in a lower energy barrier and a more favourable hopping mechanism through the molecules. Segal, M. Material history: Learning from silicon. Nat. 2012 4837389 483, S43–S44 (2012).Koch, N. Opportunities for energy level tuning at inorganic/organic semiconductor interfaces. Appl. Phys. Lett. 119, 260501 (2021). Figure 1