Mitigation of Electrical Failure of Silver Nanowires under Current Flow and the Application for Long Lifetime Organic Light‐Emitting Diodes

Abstract

The extended lifetime of organic light‐emitting diodes (OLEDs) based on enhanced electrical stability of a silver nanowire (AgNW) transparent conductive electrode is reported. Specifically, in depth investigation is performed on the ability of atomic layer deposition deposited zinc oxide (ZnO) on AgNWs to render the nanowires electrically stable during electrical stressing at the range of operational current density used for OLED lighting. ZnO‐coated AgNWs have been observed to show no electrical, optical, or morphological degradation, while pristine AgNW electrodes have become unusable for optoelectronic devices due to dramatic decreases in conductivity, transparency, and fragmentation of the nanowire network at ≈150 mA cm−2. When fabricated into OLED substrates, resulting OLEDs fabricated on the ZnO‐AgNW platform exhibit a 140% increase in lifetime when compared to OLEDs fabricated on indium tin oxide (ITO)/glass, and ≈20% when compared to OLEDs fabricated on AgNW based substrates. While both ZnO‐coated and pristine AgNW substrates outperform ITO/glass due to the lower current densities required to drive the device, morphological stability in response to current stressing is responsible for the enhancement of lifetime of ZnO‐AgNW based OLEDs compared to pristine AgNW based OLEDs.

Releasing the Trapped Light for Efficient Silver Nanowires‐Based White Flexible Organic Light‐Emitting Diodes

“…As a result, an optimized AgNW‐based FTE shows an optical transmittance of 84.5% (at 550 nm), a haze of 3.3% (at 550 nm), a sheet resistance of ≈20.5 Ω sq −1 , and an averaged surface roughness of ≈19.8 nm. To alleviate the surface roughness of AgNWs and avoid possible interelectrode shorting between protuberant nodes of AgNWs and the top metal electrode, a sol–gel‐derived ZnO layer was used to planarize the surface of AgNWs because of its wide optical bandgap for light transmission, high electron mobility for charge transport, and low‐temperature solution processability . Moreover, it has been demonstrated that the junction resistance of ZnO‐welded AgNWs can be significantly reduced, with their heat stability also improved .…”

“…To alleviate the surface roughness of AgNWs and avoid possible interelectrode shorting between protuberant nodes of AgNWs and the top metal electrode, a sol–gel‐derived ZnO layer was used to planarize the surface of AgNWs because of its wide optical bandgap for light transmission, high electron mobility for charge transport, and low‐temperature solution processability . Moreover, it has been demonstrated that the junction resistance of ZnO‐welded AgNWs can be significantly reduced, with their heat stability also improved . The dual‐side patterning of ZnO layers was conducted via a thermal nanoimprinting technique with a polydimethylsiloxane (PDMS) mold to form nanocone‐style aperiodic arrays.…”

Emerging Novel Metal Electrodes for Photovoltaic Applications

“…While thermal annealing on the transparent electrode will produce a uniform distribution of heat on the entire surface, joule heat is majorly generated from the contact regions, which have large resistance as compared to the crystalline metal NWs. The rapid accumulation of heat in these regions will induce breakdown at the contact and increase the resistance of transparent electrode after long‐time electrical bias . Soldering the contact of Ag NWs by crystalline Ag materials would definitely decrease the contact resistance and lead the uniform generation of joule heat from the entire electrode, which helps to improve the stability of the transparent electrode under electrical bias .…”

“…On the other hand, joule heat generated at the contact region will be quickly dissipated to the surrounding area due to the high thermal conductivity of 2D carbon materials, which is also helpful to improve the thermal stability of metal nanowire based transparent electrode . Additional metal oxide coating on metal NWs is also beneficial for the enhancement of thermal stability of transparent electrode due to the high melting point of metal oxide, which will restrain the deformation of metal NWs …”

12‐1: Invited Paper: Stretchable Transparent Electrodes Based on Silver Nanowires

“…Electromigration of silver is often a concern for the use of AgNWs in TCE. Measuring the sheet resistance of the AgNW TCE did show degradation at elevated temperature or high current density [11,12]. This shortcoming could be addressed by the use of an extra coating of ZnO deposited by atomic layer deposition (ALD).…”