Abstract
In this study, we performed metal (Ag, Ni, Cu, or Pd) electroplating of core–shell metallic Ag nanowire (AgNW) networks intended for use as the anode electrode in organic light-emitting diodes (OLEDs) to modify the work function (WF) and conductivity of the AgNW networks. This low-cost and facile electroplating method enabled the precise deposition of metal onto the AgNW surface and at the nanowire (NW) junctions. AgNWs coated onto a transparent glass substrate were immersed in four different metal electroplating baths: those containing AgNO3 for Ag electroplating, NiSO4 for Ni electroplating, Cu2P2O7 for Cu electroplating, and PdCl2 for Pd electroplating. The solvated metal ions (Ag+, Ni2+, Cu2+, and Pd2+) in the respective electroplating baths were reduced to the corresponding metals on the AgNW surface in the galvanostatic mode under a constant electric current achieved by linear sweep voltammetry via an external circuit between the AgNW networks (cathode) and a Pt mesh (anode). The amount of electroplated metal was systematically controlled by varying the electroplating time. Scanning electron microscopy images showed that the four different metals (shells) were successfully electroplated on the AgNWs (core), and the nanosize-controlled electroplating process produced metal NWs with varying diameters, conductivities, optical transmittances, and WFs. The metal-electroplated AgNWs were successfully employed as the anode electrodes of the OLEDs. This facile and low-cost method of metal electroplating of AgNWs to increase their WFs and conductivities is a promising development for the fabrication of next-generation OLEDs.
Highlights
The replacement of indium tin oxide (ITO) with metal nanowires (e.g. silver nanowires (AgNWs), copper nanowires, gold nanowires) in the fabrication of transparent conductive electrodes (TCEs) has been investigated in the past decades [1,2,3,4,5,6]
Pt mesh with inert and high exchange current density property was utilized as anode electrode, preventing slow oxidation reaction from low exchange current density property which can result in difficulty on controlling the growth rate of electroplating [40,41,42]
The primary metal source provided metal ions for the deposition of the metal element onto the Ag nanowire (AgNW) surface; the conductivity enhancer enabled rapid movement of the metal ions in the electroplating solution; and the pH buffer had the important function of suppressing the decrease in pH of the solution
Summary
The replacement of indium tin oxide (ITO) with metal nanowires (e.g. silver nanowires (AgNWs), copper nanowires, gold nanowires) in the fabrication of transparent conductive electrodes (TCEs) has been investigated in the past decades [1,2,3,4,5,6]. Several post-welding methods for minimizing the contact resistance at the NW junctions have been explored with the aim of reducing the high sheet resistance of the as-coated AgNW electrode Examples of such methods include welding using heat energy (e.g., thermal welding, plasmonic welding, and Joule heating), chemical reduction, and electrochemical metal deposition [27,28,29,30,31,32,33,34,35,36,37,38]. The device with a high-WF and low-resistance Ni-AgNW anode exhibited even higher efficiency (11.60 cd/A, 7.90 lm/W and 4.63%) than an OLED with the conventional ITO anode (9.51 cd/A, 4.05 lm/W and 3.80%) This simple and low-cost metal electroplating method for adjusting the WFs and conductivities of the AgNW electrodes has great potential to be used in the fabrication of next-generation optoelectronic devices
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