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.
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.
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