Synthesis and Applications of Silver Nanowires for Transparent Conductive Films

Abstract

Flexible transparent conductive electrodes (TCEs) are widely applied in flexible electronic devices. Among these electrodes, silver (Ag) nanowires (NWs) have gained considerable interests due to their excellent electrical and optical performances. Ag NWs with a one-dimensional nanostructure have unique characteristics from those of bulk Ag. In past 10 years, researchers have proposed various synthesis methods of Ag NWs, such as ultraviolet irradiation, template method, polyol method, etc. These methods are discussed and summarized in this review, and we conclude that the advantages of the polyol method are the most obvious. This review also provides a more comprehensive description of the polyol method for the synthesis of Ag NWs, and the synthetic factors including AgNO₃ concentration, addition of other metal salts and polyvinyl pyrrolidone are thoroughly elaborated. Furthermore, several problems in the fabrication of Ag NWs-based TCEs and related devices are reviewed. The prospects for applications of Ag NWs-based TCE in solar cells, electroluminescence, electrochromic devices, flexible energy storage equipment, thin-film heaters and stretchable devices are discussed and summarized in detail.

Keywords: flexible device; inkjet printing; polyol method; silver nanowires; transparent conductive electrodes.

Figure 1

Properties and applications of recently developed devices based on Ag NWs TCE. “Heat management”, reproduced with permission [14]. Copyright 2015, ACS Nano. “Heat TCF” means “Heat Transparent conductive film”, reproduced with permission [15]. Copyright 2019, ACS Applied Materials & Interfaces. “Organic light emitting diode (OLED)”, reproduced with permission [16]. Copyright 2017, Nanotechnology. “Stretchable LED”, reproduced with permission [17]. Copyright 2017, Current Applied Physics. “Solar cell”, reproduced with permission [18]. Copyright 2016, Journal of Materials Chemistry A. “TCF”, reproduced with permission [19]. Copyright 2016, Solar Energy Materials and Solar Cells. “TCE”, reproduced with permission [20]. Copyright 2017, Solar Energy Materials and Solar Cells. “Heater”, reproduced with permission [21]. Copyright 2018, Nanoscale.

Figure 2

Synthesis of Ag NWs and some influencing factors: (a) Diameters and lengths of the Ag NWs as a function of the molar ratio of PVP/AgNO₃ and transmission electron microscope (TEM) image of Ag nanostructures obtained with 0.5 mL of Ag seeds added [45]. Copyright 2004, Crystal Growth. (b) Schematic representation of the polyol synthesis of Ag NWs [58]. Copyright 2016, Materials Chemistry and Physics. (c) Schematic of the different concentrations of AgNO₃ for synthesis of Ag NWs with different diameters [54]. Copyright 2014, Solid State Chemistry. (d) Schematic illustration of template synthesis procedures for obtaining the AgI/Ag heterojunction structures [84]. Copyright 2007, Advanced Functional Materials.

Figure 3

The schematic illustration of the preparation of Ag NWs/ZnO composite TCE and the sheet resistance, transmittance at 550 nm and figure of merit for the Ag NWs TCEs with different spin-coating cycles of ZnO, respectively [91]. Copyright 2018, Journal of Alloys and Compounds.

Figure 4

Two preparation methods of Ag NWs TCE. (a) Fabrication processes of the hybrid electrode on a photopolymer substrate [98]. Copyright 2017, Organic Electronics. (b) Schematic illustration of the RTR fabrication process for the embedded Ag NWs TCE on PET film [102]. Copyright 2017, Organic Electronics.

Figure 5

Solutions to the problems of high junction resistance, poor mechanical stability and poor thermal/environmental stability in Ag NWs TCE preparation: (a) SEM images of pristine Ag NWs, NaAlg/Ag NWs composite film, NaAlg/Ag NWs composite film after mechanical pressing and NaAlg/Ag NWs composite film after mechanical pressing and CaCl₂ treatment and the schematic diagrams of junction between Ag NWs corresponding to SEM images, and the schematic illustration of a possible mechanism of crack renovation [104]. Copyright 2017, ACS Applied Materials and Interfaces. (b) Schematic of moisture treatment for capillary-force-induced cold welding of Ag NWs [103]. Copyright 2017, Nano Letters. (c) The 3D (left) and sectional (right) schematic peel-assembly-transfer (PAT) procedure for the insertion of the PEI/PAA adhesion multilayer between Ag NWs and PET substrates. (d) The prepared Ag NWs TCF on PET substrate indicating that the film is transparent and flexible, and the transmittance spectra of the Ag NWs network before and after PAT process [109]. Copyright 2017, Langmuir.

Figure 6

Some applications of the Ag NWs TCE. (a) Schematic illustration showing the preparation process of NC LDH NSs@Ag@CC by a single-step electrochemical deposition (ECD) process [115]. Copyright 2017, Nano Energy. (b) Preparation of the conductive and scattering flexible substrates [119]. Copyright 2017, Organic Electronics. (c) Photographs of the light emission of the Ru-based ECL displays with a Ag NWs electrode (top), PEDOT:PSS/Ag NWs hybrid electrode (middle), and T-PEDOT:PSS/Ag NWs hybrid electrode (bottom) and the ECL spectra of the flexible Ru-based ECL displays with the three types of electrodes and the relative change in the intensity of the flexible Ru-based ECL displays with the three types of electrodes as a function of bending cycles [118]. Copyright 2017, Chemical Communications. (d) Fabrication and properties of Ag NFs ECSW [124]. Copyright 2017, Advanced Material.