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Slab-like copper films with a thickness of 9 nm (∼70 atoms) and sheet resistance of ≤9 sq −1 are shown to exhibit remarkable long-term stability toward air-oxidation when passivated with an 0. 8 nm aluminium layer deposited by simple thermal evaporation. The sheet resistance of 9 nm Cu films passivated in this way, and lithographically patterned with a dense array of ∼6 million apertures per cm 2 , increases by <3.5% after 7,000 h exposure to ambient air. Using a combination of annular-dark field scanning transmission electron microscopy, nanoscale spatially resolved elemental analysis and atomic force microscopy, we show that this surprising effectiveness of this layer results from spontaneous segregation of the aluminium to grain boundaries in the copper film where it forms a ternary oxide plug at those sites in the metal film most vulnerable to oxidation. Crucially, the heterogeneous distribution of this passivating oxide layer combined with its very low thickness ensures that the underlying metal is not electrically isolated, and so this simple passivation step renders Cu films stable enough to compete with Ag as the base metal for transparent electrode applications in emerging optoelectronic devices.
Patterning evaporated silver and copper films without metal removal using extremely thin printed organofluorine films to modulate metal vapour condensation.
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A powerful approach to increasing the far-field transparency of copper film window electrodes which simultaneously reduces intraband absorption losses for wavelengths <550 nm and suppresses reflective losses for wavelengths >550 nm is reported. The approach is based on incorporation of a random array of ≈100 million circular apertures per cm 2 into an optically thin copper film, with a mean aperture diameter of ≈500 nm. A method for the fabrication of these electrodes is described that exploits a binary polymer blend mask that self-organizes at room temperature from a single solution, and so is simple to implement. Additionally all of the materials used in electrode fabrication are low cost, low toxicity, and widely available. It is shown that these nanostructured copper electrodes offer an average far-field transparency of ≥80% and sheet resistance of ≤10 Ω sq −1 when used in conjunction with a conventional solution processed ZnO electron transport layer and their utility in inverted organic photovoltaic devices is demonstrated.
Silver nanowire networks can offer exceptionally high performance as transparent electrodes for stretchable sensors, flexible optoelectronics, and energy harvesting devices. However, this type of electrode suffers from the triple drawbacks of complexity of fabrication, instability of the nanowire junctions, and high surface roughness, which limit electrode performance and utility. Here, a new concept in the fabrication of silver nanowire electrodes is reported that simultaneously addresses all three of these drawbacks, based on an electrospun nanofiber network and supporting substrate having silver vapor condensation coefficients of one and near‐zero, respectively. Consequently, when the whole substrate is exposed to silver vapor by simple thermal evaporation, metal selectively deposits onto the nanofiber network. The advantage of this approach is the simplicity, since there is no mask, chemical or dry metal etching step, or mesh transfer step. Additionally, the contact resistance between nanowires is zero and the surface roughness is sufficiently low for integration into organic photovoltaic devices. This new concept opens the door to continuous roll‐to‐roll fabrication of high‐performance fused silver nanowire electrodes for myriad potential applications.
Ga-doped zinc oxide (GZO) films were deposited using rf magnetron sputter deposition and a Ga2O3(5 wt %)-doped ZnO ceramic target under various deposition conditions. The effects of each deposition condition on the electrical, structural, and optical properties of the GZO films were investigated to obtain a transparent conducting oxide (TCO) with a high transmittance and a low resistivity for a-Si:H thin-film solar cells. Resistivity showed a strong dependence on working pressure and rf power. The lowest resistivity of 1.9×10-4 Ω·cm was obtained at an rf power density of 2.47 W/cm2. The highest figure of merit for the use of TCO was achieved in the 800-nm-thick GZO film [ρ=2.1×10-4 Ω·cm, average transmittance (400–800 nm) = 92.1%] deposited at 10 mTorr and an rf power density of 1.85 W/cm2. These results indicate that the high-performance TCO fabricated in this work is suitable for use as a transparent electrode layer for thin-film solar cells.
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