Year-end Sale % OFF 
Abstract
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 one hundred 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 using a copper based transparent electrode, outperforming identical devices using ITO coated plastic as the transparent electrode.
Highlights
The low cost associated with processing organic semiconductors by printing, together with the low processing temperature and color tuneability make organic photovoltaics (OPVs) attractive for a diverse range of applications (Kippelen et al, 2009; Ierides et al, 2019)
The PS phase was selectively removed using cyclohexane, followed by a UV/O3 treatment to open out the base of the holes in the PMMA, and rapid etching and removal of the PMMA mask according to our previously-reported protocol designed for glass substrates (Pereira et al, 2018; Figures 1, 2A–D)
Using a dipping rate of 2 mm s−1 and a dwell time of 2 s a very similar aperture size distribution to that achieved by spin coating can be achieved, even though the solvent evaporation rates for spin coating at 2,500 rpm and dipcoating are very different, which demonstrates the robustness of this method for mask formation and the scope for increasing the dipping speed
Summary
The low cost associated with processing organic semiconductors by printing, together with the low processing temperature and color tuneability make organic photovoltaics (OPVs) attractive for a diverse range of applications (Kippelen et al, 2009; Ierides et al, 2019). In addition to requiring a high Haacke FoM, flexible OPVs require a transparent electrode that does not degrade when bent, both for application purposes and for compatibility with roll-to-roll processing. Parasitic absorption in Cu due to inter-band absorption losses mean that optically-thin Cu films are not as transparent as Ag films of the same thickness (Burdick, 1963; West et al, 2010; Pereira et al, 2017, 2018) To address this we have recently reported a powerful bio-inspired method for increasing the far-field transparency of optically-thin Cu films on glass, based on incorporating a random distribution of ∼100 million sub-micron diameter holes cm−2 which simultaneously reduces absorption losses whilst suppressing losses due to reflection (Pereira et al, 2018). We advance that work by showing that: (i) the method of electrode fabrication can be translated to the a technologically important transparent plastic substrate polyethylene terephthalate (PET) with only slight adaptation, and that the Haacke FoM can be increased substantially above that previously-reported on glass substrates with a small increase the aperture density; (ii) it is possible to fabricate the polymer mask by dip coating, which, unlike spin coating, is a scalable deposition method compatible with roll-to-roll processing; (iii) these electrodes outperform ITO coated plastic as the transparent electrode in flexible OPVs
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
