(Invited) Hybrid Interfaces: Ni Electrodeposition on Top of PCPDT-BT
Authors: Fontanesi Claudio , Stefani Andrea , Pasquali Luca 
Published: February 2024

The study of physical and chemical properties of hybrid (inorganic/organic) interfaces is a particularly intriguing field of science.1,2 What is more, in principle possible technological applications are of huge interest, which is due to the use of these materials as semiconductors in the area of photovoltaics, sensors and organic electronics. In this work the attention is focused on two materials to be coupled nickel and poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDT-BT). Nickel is of great interest because of its ferromagnetic property (exploited as both a spin-injector in electronics and as a working electrode in spin-dependent electrochemistry, SDE3). PCPDT-BT is one of the most promising thiophene based candidates for use in organic electronics, its dielectric/conductive state can be driven by suitable doping, conduction is due to polarons4. The PCPDT-BT molecular structure is shown in Figure 1a. Figure 1b shows the chrono amperometry (CA) curve (inset is a cyclic voltammetry (CV) curve recorded before Ni electrodeposition) recorded using a PCPDT-BT working electrode in a typical Watt’s bath5: 150 g/L of nickel sulphate, 60 g/L nickel chloride, 37 g/L boric acid, pH = 5.
The massive Ni electrodeposition (thickness of about 2 mm) was obtained by applying a constant -1.7 V potential for 500 seconds, Figure 1b sets out the relevant experimental curve (the inset in Figure 1b shows a CV recorded before Ni electrodeposition, used to determine the suitable reduction potential to be used in the CA. Figure 1c and 1d show impedance (EIS) data recorded just after the Ni electrodeposition (wet sample Figure 1c, with the base electrolyte still present within the PCPDT-BT) and after careful drying the sample (Figure 1d). Please note that 1) clearly there is not any short-circuit in between the Ni and the Au substrate 2) EIS data of the “wet” state are compatible with doped polymer conductivity 3) EIS data “dry” state are definitively more typical of a dielectric material (de-doped). At present, in our laboratory the electrodeposition of Ni on PCPDT-BT is under investigation as a function of different experimental preparation strategies, to find a rationale in the relevant electronic properties.
All in all, the overall electrochemical behavior indicates that the electrodeposited nickel coating is of good quality, at least comparable with coatings obtained via magnetron sputtering, evaporation or e-beam. The latter experimental methods suffer of the need of vacuum conditions for obtaining the metal coating, which is a major complication with respect to electrodeposition from water solution. A further advantage of electrochemical methods is the “low” temperature, while vacuum based methods tend to destroy the organic layer.
Figure 1. a) PCPDT-BT molecular structure. b) typical chronoamperometric Ni on PCPDT-BT electrodeposition curve (inset: CV recorded just prior the chronoamperometry). Impedance of the Ni/PCPDT-BT hybrid interface, Bode plot: wet d) impedance of the Ni/PCPDT-BT hybrid interface: dry.

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Figure 1