Abstract
In recent years, many research groups have synthesized ultra-thin silver nanowires (AgNWs) with diameters below 30 nm by employing Cl− and Br− simultaneously in the polyol process. However, the yield of AgNWs in this method was low, due to the production of Ag nanoparticles (AgNPs) as an unwanted byproduct, especially in the case of high Br− concentration. Here, we investigated the roles of Cl− and Br− in the preparation of AgNWs and then synthesized high aspect ratio (up to 2100) AgNWs in high yield (>85% AgNWs) using a Cl− and Br− co-mediated method. We found that multiply-twinned particles (MTPs) with different critical sizes were formed and grew into AgNWs, accompanied by a small and large amount of AgNPs for the NaCl and NaBr additives, respectively. For the first time, we propose that the growth of AgNWs of different diameters and yields can be understood based on the electron trap distribution (ETD) of the silver halide crystals. For the case of Cl− and Br− co-additives, a mixed silver halide crystal of AgBr1−xClx was formed, rather than the AgBr/AgCl mixture reported previously. In this type of crystal, the ETD is uniform, which is beneficial for the synthesis of AgNWs with small diameter (30~40 nm) and high aspect ratio. AgNW transparent electrodes were prepared in air by rod coating. A sheet resistance of 48 Ω/sq and transmittance of 95% at 550 nm were obtained without any post-treatment.
Highlights
Silver nanowires (AgNWs) have attracted much attention for use in devices like flexible touch screens, thin film solar cells, organic light emitting diodes and biomolecular sensors [1,2,3,4,5]
The statistics of diameter and length of AgNWs are shown in Figure S1, illustrating that uniform AgNWs with small diameters and high aspect ratio were obtained for the NaCl/NaBr co-mediated sample
We have systematically investigated the roles of NaCl and NaBr additives in the polyol synthesis of AgNWs under ambient atmosphere
Summary
Silver nanowires (AgNWs) have attracted much attention for use in devices like flexible touch screens, thin film solar cells, organic light emitting diodes and biomolecular sensors [1,2,3,4,5]. AgBr-seeded AgNWs have a small diameter but are accompanied by many AgNPs. The large number of AgNPs (low yield of AgNWs) obtained by using NaBr additive is related to the weak etching ability of Br−/O2 compared with that of Cl−/O2. In order to increase the percentage of NWs, other factors must be considered to precisely control the synthetic process, such as bubbled gas [12], injection rate of additive and reaction temperatures [14,16,17,18] Tuning these complicated conditions to achieve high yield of AgNWs with small lateral size using Cl− or/and Br− mediated methods is still a great challenge. We propose a facile method to synthesize AgNWs with diameter of 30~40 nm, aspect ratio up to 2100 and AgNW percentage yield above 85%, using Cl− and Br− co-additives under ambient atmospheric conditions. AgNWs with an aspect ratio of ~2100 were used to form a transparent conductive electrode with excellent optical and electrical performance
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