Electroless Ni–P plating deposited simultaneously on both surface sides of a flexible indium tin oxide coated polyethylene terephthalate substrate

In this study, we propose a plating bath for electroless nickel-phosphorous (Ni–P) simultaneous deposition on both surfaces of a flexible polyethylene terephthalate (PET) substrate coated on one side with indium tin oxide (ITO). First a nucleation step is performed with tin(II) chloride and palladium(II) chloride. After this, a bath containing nickel ion source reducing agent, complexing and stabilization agents is used to deposit the Ni–P layer. The nucleation treatment used was the same for both ITO and PET surfaces, which results in a low-cost process compared to other methods. Several immersion times in the electroless bath were used to obtain the Ni–P layers onto PET and ITO surfaces. Structural, morphological and electrical properties of the samples were evaluated by optical microscopy, scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, profilometry and four-point probe method. The Ni–P film deposition rate on the PET surface (112.2 nm/min) was higher than on the ITO surface (88.8 nm/min). The effect of the annealing temperature on the electrical and morphological properties of the Ni–P films were also investigated. After heat treatment (120 °C, 1 h), the Ni–P particles coalesced, resulting in more compact films, with reduced surface roughness, and with improved conductivity. Our approach enables an innovative dual function technological solution: the Ni–P/ITO side can be used as flexible current collectors in high-power output devices (e.g., emerging photovoltaic devices such as perovskite solar cells), whereas the PET side can be used for flexible current collectors in low-power output devices (e.g., sensors and capacitors). Both surfaces can be used concomitantly, combining the two kinds of application (e.g., integration of two types of electronic devices using a unique substrate).