Copper nanoparticles (CuNPs) are attractive as a low-cost alternative to their gold and silver analogues for numerous applications, although their potential has hardly been explored due to their higher susceptibility to oxidation in air. Here we show the unexpected findings of an investigation into the correlation between the air-stability of CuNPs and the structure of the thiolate capping ligand; of the eight different ligands screened, those with the shortest alkyl chain, –(CH₂)₂–, and a hydrophilic carboxylic acid end group are found to be the most effective at retarding oxidation in air. We also show that CuNPs are not etched by thiol solutions as previously reported, and address the important fundamental question of how the work function of small supported metal particles scales with particle size. Together these findings set the stage for greater utility of CuNPs for emerging electronic applications.

We report the findings of a study into the suitability of copper (I) thiocyanate (CuSCN) as a hole-transport layer in inverted photovoltaic (PV) devices based on the black gamma phase (B-γ) of CsSnI₃ perovskite. Remarkably, when B-γ-CsSnI₃ perovskite is deposited from a dimethylformamide solution onto a 180–190 nm thick CuSCN film supported on an indium-tin oxide (ITO) electrode, the CuSCN layer is completely displaced leaving a perovskite layer with high uniformity and coverage of the underlying ITO electrode. This finding is confirmed by detailed analysis of the thickness and composition of the film that remains after perovskite deposition, together with photovoltaic device studies. The results of this study show that, whilst CuSCN has proved to be an excellent hole-extraction layer for high performance lead-perovskite and organic photovoltaics, it is unsuitable as a hole-transport layer in inverted B-γ-CsSnI₃ perovskite photovoltaics processed from solution.

The state-of-the-art technology of fabricating printed copper electronics is focussed largely on thermal sintering restricting transition towards heat sensitive flexible substrates. Herein we report a pioneering technology which eliminates the need for conventional sintering. Biopolymer-stabilised copper particles are prepared such that they can be compressed at room temperature to generate air-stable films with very low resistivities (2.05 – 2.33 × 10⁻⁸ Ω m at 20 °C). A linear positive correlation of resistivity with temperature verifies excellent metallic character and electron microscopy confirms the formation of films with low porosity (< 4.6%). An aqueous ink formulation is used to fabricate conductive patterns on filter paper, first using a fountain/dip pen and then printing to deposit more defined patterns (R < 2 Ω). The remarkable conductivity and stability of the films, coupled with the sustainability of the approach could precipitate a paradigm-shift in the use of copper inks for printable electronics.

Optically thin copper films with a random array of sub-optical wavelength apertures couple strongly with light in the wavelength range 600–800 nm due to excitation of surface plasmonic resonances. Herein we show that this trapped light can be used to excite electronic transitions in a nearby strongly absorbing organic semiconductor before the plasmonic excitations dissipate their energy as heat into the metal. This energy transfer process is demonstrated using model small molecule and polymer photovoltaic devices (based on chloro-aluminium phthalocyanine:C₆₀ and PCE-10:PC₇₀BM heterojunctions respectively) in conjunction with a nano-hole copper electrode formed by thermal annealing an optically thin Cu film supported on polyethylene terephthalate. The efficiency of this process is shown to be highest for wavelengths in the range 650–750 nm, which is part of the solar spectrum that is weakly absorbed by today's high performance organic photovoltaic devices, and so these findings demonstrate that this type of electrode could prove useful as a low cost light catching element in high performance organic photovoltaics.

We report a copper–zinc oxide bilayer electrode supported on flexible polyethylene terephthalate (PET) with a sheet resistance of 11. 3 Ω sq⁻¹ and average transparency of 84.6% in the wavelength range of 400–800 nm. The copper film is perforated with a dense array of sub-micron diameter apertures fabricated using polymer-blend lithography, which imparts broad band anti-reflectivity. We demonstrate proof-of-principle that it is possible to fabricate the polymer mask by dip coating which is a scalable deposition method compatible with roll-to-roll processing. During storage of the electrode at ambient temperature the ZnO layer is spontaneously doped with copper from the underlying copper film and so the thin ZnO layer serves both as an anti-reflecting layer and an excellent electron transport layer. When compared with commercially available indium tin oxide coated (ITO) plastic substrates this electrode exhibits superior stability towards bending deformation, with no change in sheet resistance after bending through a 4 mm radius of curvature 100 times. Model inverted organic photovoltaic (OPV) devices using this electrode exhibit a champion power conversion efficiency of ~8.7%, which is the highest reported efficiency to date for an OPV device using a copper based transparent electrode, outperforming identical devices using ITO coated plastic as the transparent electrode.