Donor Design for Maximum Mobility TCOs

Lead Research Organisation: University College London
Department Name: Chemistry

Abstract

Transparent conducting oxides (TCO) are ubiquitous in modern society, being components in a vast array of consumer electronics (e.g. smart phones, tablets, lap tops, flat panel displays etc.) and finding use in applications such as solar cells, smart windows, low emissivity windows etc. To date, the TCO with the largest share of the market is tin doped indium oxide (known as ITO), which displays excellent transparency and conductivity. The fact that indium is not very abundant in the earth's crust (and is often found in unstable geopolitical areas), allied to the inexorable increase in the demand for consumer electronics globally, has caused large fluctuations in the price of indium over the past decade. This has understandably caused concern in the industrial sector. Other TCO materials exist, such as fluorine doped tin dioxide (FTO), antimony doped tin dioxide (ATO), and Aluminium doped zinc oxide (AZO), however, they have not reached the performance levels of ITO. In each case, the limitations are linked to the dopant that is used
Recently we proposed an initial understanding of how some specific novel dopants can produce enhanced performance TCOs, termed the "remote impurity scattering mechanism", and we will now screen novel dopants in the earth abundant host oxides zinc oxide, tin dioxide and barium stannate, in order to find the ideal TCO/dopant combination.

This will be done in 3 ways:
1) Computational screening of novel dopants
2) Deposition of doped thin films using low cost, scaleable chemical vapour deposition
3) Physical characterisation of the doped films

The synergistic approach between computational chemistry, semiconductor physics and low cost scaleable deposition will result in new high performance, low cost, industrially viable TCOs. They will be transferred from our labs to industrial scale processes on our project partner's float glass line.

Planned Impact

This project and its results will have significant impact on:
1) The economy through the design and development of novel, earth abundant, transparent conducting oxides which will be competitive with the rare and expensive indium based materials that currently dominate the TCO market. Commercial and economic benefits will occur through the widespread production of these novel TCO coatings - ensuring the UK maintains a world-leading capability in the development and manufacture of transparent coatings.
2) People through the research team and the technical expertise developed throughout the project, including the training received and the range of transferable skills developed via interaction with industry, academics, engagement with the media, the general public, policy makers and legislators.
3) Knowledge since significant advances in the understanding of dopant choice for these TCO applications and film deposition will be delivered during the project.
4) Society through developing science and technology to improve quality of life. TCOs are used in every part of modern life, having applications in solar cells, smart windows, and in every touch screen/flat panel display in modern consumer electronics. A breakthrough in the understanding of TCO materials will play a vital role in the business and homes in the UK and worldwide. The identification of a dopant that can maintain a higher mobility in these earth abundant TCOs will alter the landscape for TCO production worldwide, ensuring that costs will decrease, and modern consumer electronics will become more affordable. The knock on effect from this on global quality of life will be huge.

The Beneficiaries: This research project will benefit:
(i) General public: There is a huge market demand for cheaper alternatives to indium-based transparent electrodes in modern consumer electronics. Fabrication of a doped TCO that is competitive in terms of performance will dramatically alter the price-per-kg statistics, meaning that consumer electronics will become much more affordable. In addition, gas sensors are typically based on doped TCOs, and this project could also yield new and improved gas sensors, to improve quality of life.
(ii) Commercial sector: The global market for transparent coatings is forecast to increase from $4.8 billion in 2013 to $7.1 billion in 2018. Therefore, there is significant pressure to supply large volumes of improved sustainable TCO coatings suitable to meet the varied requirements that thin film solar cell manufacturers demand. The UK is at the forefront of the transparent coatings field, with NSG currently the world's largest supplier of TCO glass, depositing approximately 7 million m2 of TCO coated glass per annum in the UK alone. Globally, the move towards In-free electronics has been adopted, but with very little commercial success. The novel doping techniques predicted in this project will ensure that the UK will be the global leaders in transparent coatings in the In-free age. Other industry would also benefit through the expansion of TCOs, which are used in automotive glazing, photovoltaic powered displays, security panels, consumer electronics, and solar panels. Indeed NSG are also a supplier to First Solar, the leaders in the thin film photovoltaics sector, a sector which has been experiencing excellent growth.
(iii) Environment: The development of alternative energy sources, such as solar-power, is clearly of great importance. The development of a novel high performance, earth abundant TCO will alter the price-metrics for solar cells. This will allow cheaper solar modules, bringing down the cost of renewable energy for the UK and the world. The ability to generate electricity affordably with a very low environmental footprint will aid the UK government to hit its targets in respect to reduction of greenhouse gases, and will have a global impact also.

Publications

10 25 50
 
Description We have discovered a new doping mechanism for transparent conducting oxides (TCOs), which could lead to higher mobility and higher performance TCOs for a range of applications including low-emmisivity windows and solar cells. We are currently doing control experiments (using theory and experiment) and expanding the number of dopants that can act in this way, putting the physical understanding of this new mechanism on a firm footing, so that we can move forward with our industrial partners Pilkington NSG. We are not even one year into the grant, and we already have multiple manuscripts i preparation. We have identified that Mo is the ideal dopant for In2O3, and no Sn, which is the industry standard material. We have submitted a publication on this, which we expect will be high impact. We have also now completed detailed experiments on other novel dopants for In2O3, providing more proof of our doping mechanism, which are also being written up for publication. We have used this new understanding of the doping mechanism to search for novel dopants for SnO2, and have identified the optimum dopant for this system. Preliminary experiments using Aerosol Assisted CVD have demonstrated that the dopant does yield higher mobility samples than either fluorine or antimony doped SnO2. We are now attempting to recreate these results using atmospheric pressure CVD which is what Pilkington NSG use on their plans. If this is successful, we will move to large scale trials at Pilkington NSGs factory.
Exploitation Route Pilkington NSG will scale up any new TCO systems that emanate from our work, and will test them on their float glass line. This has the possibility to add another product line to their doped SnO2 systems.
Sectors Construction,Electronics,Energy,Manufacturing, including Industrial Biotechology,Transport