Abstract: Photovoltaics (PVs) fabricated by printing at low temperature onto flexible substrates are attractive for a broad range of applications in buildings and transportation, where flexibility, colour-tuneability, light-weight and low cost are essential requirements. Two emerging PV technologies that have strong potential to meet these requirements are organic PVs and perovskite PVs. However, it is widely recognised that these classes of PV can only fulfil their full cost advantage and functional advantages over conventional thin film PVs if a suitable transparent, flexible electrode is forthcoming. Indium-tin oxide (ITO) is currently the dominant transparent conductor used in opto-electronics, including PVs. However, its fragile ceramic nature makes it poorly compatible with flexible substrates and indium has been identified as a ‘critical raw material’ for the European economic area, due to the high risk of supply shortage expected in the next 10 years. Consequently there is a need to develop a viable alternative to ITO, particularly for utility in emerging PVs large for which quantities will be needed in the coming decades to help address the threat posed by rapid global warming. Grids and fused nanowire networks of the most electrically conductive metal, silver, can perform as well as ITO as a transparent electrode in PVs. However, conventional methods for fabricating these types of electrodes involve printing or spraying costly solutions of metal nanoparticles, or selective removal of metal by etching using harmful chemicals, or by electrochemical deposition - an inherently chemical intensive and slow solution based process. This talk will present a new approach to the fabrication of high performance transparent electrodes based on both grids and fused nanowire networks of these metals, and demonstrate utility in organic PVs. These electrodes offer a far-field transparency > 80% and sheet resistance ≤ 5 ohm sq^-1 on flexible plastic substrates, performance that far exceeds that of ITO coated plastic. The new approach described is based on the finding that silver does not condense onto certain organofluorine compounds, so these metals can be selectively deposited by thermal evaporation without a mask. The beauty of this approach lies in its simplicity and versatility, since vacuum evaporation of metals is a well-established and widely available metal deposition method, and the shape and size of the metal features deposited is limited only by the dimensions of the organofluorine free domains. This new approach avoids the use of harmful chemical etchants and critical raw materials, and leaves the metal surface uncontaminated.
