Sustainable Manufacturing of Transparent Conducting Oxide (TCO) Inks and Thin Films

This project seeks to develop processes and resources towards sustainable and inexpensive high quality transparent conducting oxide (TCO) films (and printed tracks) on float glass, plastics and steel. In particular replacement materials for Indium Tin Oxide (ITO) and F-doped Tin Oxide (FTO). These materials are used in low-e window coatings (>£5B pa), computers, phones and PV devices. The current electronics market alone is worth in excess of £0.9 Trillion and every tablet PC uses ca 3g of tin. Indium is listed as a critical element- available in limited amounts often in unstable geopolitical areas. Tin metal has had the biggest rise in price of any metal consecutively in the last four years (valued at >£30K per ton) and indium is seen as one of the most difficult to source elements. In this project we will develop sustainable upscaled routes to TCO materials from precursors containing earth abundant elements (titanium, aluminium, zinc) with equivalent or better figures of merit to existing TCOs.

Our method uses Aerosol assisted (AA) CVD to develop large scale coatings and developing new manufacturing approach to printed TCOs using highly uniform nanoparticle dispersions. AACVD has not been upscaled- although the related Atmospheric pressure (AP) CVD is widely used industrially. APCVD was developed in the UK (Pilkington now NSG) for commercial window coating methods- and in the UK glass industry supports >5000 jobs in the supply chain. Our challenge is to take our known chemistry and develop the underpinning science to demonstrate scale up routes to large area coatings. This will include pilot scale AACVD, nanoparticle dispersions and inks. Common precursor sets will be utilized in all the techniques. Our focus will be to ensure that the UK maintains a world-leading capability in the manufacturing of and with sustainable TCOs. This will be achieved by delivering two new scale up pathways one based on AACVD- for large area coatings and inks and dispersions for automotive and PC use.

We will use known and sustainable metal containing precursors to deposit TCOs that do not involve rare elements (e.g. based on Ti, Zn, Al). Key issues will be (1) taking the existing aerosol assisted chemical vapour deposition (AACVD) process from small lab scale to a large pilot lab scale reactor (TRL3) and (2) developing a new approach to TCOs from transparent nanoparticle dispersions synthesized in a continuous hydrothermal flow systems (CHFS) reactor using an existing EPSRC funded pilot plant process (kg/h scale). Nano-dispersions will be formulated for use by the rest of the team, in jet and screen printing, advanced microwave processing and TCO application testing. Industry partners will provide engineering support, guidance on the aerosol transport issues, scale up and dynamic coating trials (Pilkington now NSG), jet and screen printing on glass (Xaar, Akzo Nobel, CPI) and use the TCO targets for Magnetron Sputtering of thin films on plastics (Teer Coatings). The two strands will be overseen by Life-cycle modelling and cost benefit analyses to take a holistic approach to the considerations of energy, materials consumption and waste and, in consultation with key stakeholders and policy makers, identify best approaches to making improvement or changes, e.g. accounting for environmental legislation in nanomaterials, waste disposal or recyclability of photovoltaics. We believe there is a real synergy of having two strands as they are linked by common scale up manufacturing issues and use similar process chemistries and precursors.

The research in this project will clearly have impact on:

> Society, by developing science and technology to improve quality of life. For example, solar energy panels offer alternative energy harvesting solutions. NSG's transparent conducting oxide (TCO) glass is used in the manufacture of panels for direct conversion of solar radiation to electricity, and TCO films find application in tablets, smartphones and electronic devices.

> The Economy, through the design and development, in partnership with leading UK companies, to develop new sustainable / scalable manufacturing methods for forming TCOs. Commercial and economic benefits will occur through developments in processing methods towards upscale manufacture of alternative TCOs on substrates, replacing rare and unsustainable elements with more earth abundant elements. This will ensure the UK maintains a world-leading capability in the manufacturing of sustainable ITO alternatives (will be ~20% of the TCO market, worth $925 million by 2016).

> Knowledge, both academic and commercial, since significant advances in alternative precursor strategies, paint and ink preparation and thin film deposition, and partial scale-up of TCOs will be delivered during the project.

> People, through the expertise developed by the research team, including the training received and the range of transferable skills developed via interactions with industry, academics, engagement with the media, the general public, policy makers and legislators.

In addition to the obvious benefits to academic researchers in the field, the research will benefit in particular, (i) the UK and global commercial sector, but also, (ii) the general public, (iii) the public sector, and, more speculatively, (iv) voluntary workers and charities.

> The Commercial Sector
The thin film solar market is predicted to grow six-fold over the next 5 years to 2GW by 2015. As such, there is pressure to supply large volumes of improved sustainable TCO coatings with properties that meet the differing requirements that thin film solar-cell manufacturer's demand. NSG are the world's largest supplier of TCO glass and therefore will benefit via technology developments during this project. Other industry will also benefit, through development of TCO sputtering targets for thin films (e.g. Teer Coatings) or TCOs inks which can be used for printed electronics, architectural smart coatings, etc.

> The General Public
Conducting oxides are critical for solar energy panels that offer alternative energy solutions, from small-scale domestic installations to large-scale solar power stations. Thin film PV modules produce power at low cost per watt and generate consistent power, even on cloudy, overcast days and at low sun angles. With increasing fuel costs, photovoltaics (PVs) are effective at reducing fuel bills and paying back the cost of installation. Improved sustainable TCO films are a key component of these PVs in the future and their development will benefit the public, e.g. supplying electricity with a very low environmental footprint

> Government/Public Sector
The reduction of fuel costs and the development of improved TCOs will have significant impact on the public sector. With increasing legislation in place via international agreements to reduce greenhouse gases to acceptable levels the development of alternative energy, such as solar-power is clearly of great importance and will reduce the need for fossil fuels. TCO films are a critical requirement for all PV devices.

> Third Sector
More speculative beneficiaries of this research are charities and voluntary organisations. With climate change leading to more frequent weather-induced disasters, the call on voluntary aid organisations is increasing. The ability to remotely generate energy from the sun using PVs will allow energy generation in areas with no access to grid power (including disaster zones).