Superstable Transparent Conductive Cu@Cu₄Ni Nanowire Elastomer Composites against Oxidation, Bending, Stretching, and Twisting for Flexible and Stretchable Optoelectronics

Abstract

Low cost and high conductivity make copper (Cu) nanowire (NW) electrodes an attractive material to construct flexible and stretchable electronic skins, displays, organic light-emitting diodes (OLEDs), solar cells, and electrochromic windows. However, the vulnerabilities that Cu NW electrodes have to oxidation, bending, and stretching still present great challenges. This work demonstrates a new Cu@Cu4Ni NW conductive elastomer composite with ultrahigh stability for the first time. Cu@Cu4Ni NWs, facilely synthesized through a one-pot method, have highly crystalline alloyed shells, clear and abrupt interfaces, lengths more than 50 μm, and smooth surfaces. These virtues provide the NW-elastomer composites with a low resistance of 62.4 ohm/sq at 80% transparency, which is even better than the commercial ITO/PET flexible electrodes. In addition, the fluctuation amplitude of resistance is within 2 ohm/sq within 30 days, meaning that at ΔR/R0 = 1, the actual lifetime is estimated to be more than 1200 days. Neither the conductivity nor the performances of OLED with elastomers as conductive circuits show evident degradation during 600 cycles of bending, stretching, and twisting tests. These high-performance and extremely stable NW elastomeric electrodes could endow great chances for transparent, flexible, stretchable, and wearable electronic and optoelectronic devices.

A Review of Conductive Metal Nanomaterials as Conductive, Transparent, and Flexible Coatings, Thin Films, and Conductive Fillers: Different Deposition Methods and Applications

“…Moreover, the composite prepared using Cu NW as filler not only presented high conductivity, great optical transparency, and excellent flexibility, but also exhibited oxidation resistance [50]. Application of Cu NW as filler in AZO is also promising for producing a composite with low sheet resistance (35.9 Ω/sq) and high optical transparency (83.9% at 550 nm), and the Cu NW/AZO composite maintained its performance even after 1280 bending cycles with a bending radius of 2.5 mm (Figure 14) [51]. From the results above, it can be concluded that Cu NPs and NWs could be good candidates for industrial-scale production of conductive metal nanomaterials, with the one obstacle of a low aspect ratio.…”

Deformable and Transparent Ionic and Electronic Conductors for Soft Energy Devices

“…Song et al fabricated Cu@Cu 4 Ni core-shell structures and embedded such NWs into PDMS, which showed enhanced stability against oxidation with unchanged resistance over 30 d (Figure 3i). [91] In addition, Cu@Ag core-shell structures were synthesized and showed stable performance over 30 d. [92] Moreover, various metal shell (Ti, Zn, V) coatings were conducted on Cu NWs, presenting an unchanged resistance over 100 d. [93] …”

Nanomaterial-based stretchable and transparent electrodes

“…These chemical and thermal instabilities of CuNWs are the main challenges to their use as stretchable and transparent electrodes. Thus, to solve these problems, a variety of reports have introduced stretchable and transparent electrodes with hybrid structures of CuNWs and other materials, such as carbon nanomaterials, conductive polymers, and metal-based materials [44,[47][48][49][50][51][52]. Graphene, a representative carbon nanomaterial, has high mechanical strength and thermal resistance and low water vapor and oxygen permeability [48][49][50].…”

“…For example, CuNWs coated with highly crystalline Cu 4 Ni alloy can be obtained through the one-pot method [51]. This Cu-Cu 4 Ni-nanowirebased transparent electrode achieved 62.4 /sq sheet resistance and 80% optical transmittance.…”