High-Performance Transparent Copper Grid Electrodes Fabricated by Microcontact Lithography for Organic Photovoltaics

Bellchambers, Philip; Varagnolo, Silvia; Maltby, Corinne and Hatton, Ross A. (2021). High-Performance Transparent Copper Grid Electrodes Fabricated by Microcontact Lithography for Organic Photovoltaics. ACS Applied Energy Materials, 4(4) pp. 4150–4155.

DOI: https://doi.org/10.1021/acsaem.1c00469

Abstract

We report high-performance transparent copper grid electrodes on glass and plastic substrates that offer a higher Haacke figure-of-merit than conventional indium tin oxide electrodes and are well-matched to the requirements for organic photovoltaics (OPVs). The electrode is fabricated using microcontact lithography with a combination of molecular resist and low toxicity etchant, namely, hexadecanethiol and aqueous ammonium persulfate. This approach to electrode fabrication is much faster than conventional lithography because it takes <2 s to print the molecular resist layer and tens of seconds to etch the copper film, with both processes performed in ambient air. The grid line width achieved is >20 times narrower than is possible using conventional metal printing methods and so a grid pitch <30 μm is easily achieved without increasing metal coverage. The very small grid-line spacing relaxes the requirement to use highly conductive films to span the gaps between grid lines, reducing parasitic absorption losses. This is demonstrated using an extremely thin (10 nm) poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer. Additionally, we present evidence that it is not always necessarily to embed the metal grid into the substrate or to planarize with a charge-transport layer, to avoid leakage current across the OPV device.

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