Presented by

Cassidy Northway

Supervised by

Dr. Kenneth Chau

Next Generation Nano-Structured Metal Oxide Electrochromic Devices and their Application in Switchable Windows

• What I did and Why

• Switchable Electrochromic Windows

• Nano-structuring

• Barriers to Implementation

• Promising Results

• Conclusion

Outline

• Completed a literature review

• 2012-present

• Metal oxides EC layers

• Nano-structured

• Focusing on application and implementation in switchable windows

What I Did

• Windows allow users to connect with the exterior environment

• Windows cause up to 75% of a building peak cooling demand [1]

• Traditional solutions (blinds and shutters) reduce visibility

• Is their a solution which maintains visibility while reducing heat transfer?

Motivation

1. Darwish, M. (2005). Kuwait Journal of Science & Engineering, 32(2), 209-222.

• Switchable or “smart” windows vary their transparence across both the visible (VIS) and near-infrared (NIR) spectra

• This is accomplished by capitalizing on chromogenic materials

• Chromogenic alter their transparency function of various stimuli ▫ Thermochromic- dependent on temperature

▫ Photochromic- dependent on ultra-violet radiation

▫ Gasochromic- dependent on exposure to reducing or oxidizing gases

▫ Electrochromic- dependent on applied voltage bias

Smart Electrochromic Windows

• Electrochromics are dominant in the literature

• Easy to operate and install (1 V DC)

• Open circuit memory

• Tunable absorption

• Operates without visible haze

Smart Electrochromic Windows

• Compare to a simple battery [2]

• A voltage bias is applied causing electron flow and ion counter-flow

• Redox reaction occurs when electrons are gained (or lost) from the EC layer and ions with opposing charge are simultaneously inserted (or extracted)

• Transported electrons facilitate intervalencetransitions, this is believed to be the cause of the change in optical properties [2]

How Electrochromic Devices Operate

2. Granqvist, C. G. et al. (2010). Thin Solid Films,518(11), 3046-3053.3. Evan, L. et al. (2014). Chemical Communications, 5(73), 1555-1574.

[3]

• The performance of an EC device is limited by the kinetic movement of the electrons and the ions as well as the availability of redox sites [4]

• Nano-structuring refers to tailoring the structure of

the EC material on the substrate

• Nano-structuring helps to reduce these limitations▫ Shortens charge transport distance

▫ Provides loss packing structure

▫ Increases surface area

Advantages of Nano-structuring

4. DOE Scientific and Technical Information (STI). (2006).Advancement of electrochromic windows United States. Dept. of Energy. Building Technology, State and Community Programs.

5. Bi, Z. et al. (2015). Materials Letters, 160, 186-189.

[5]

• Well controlled nanoporosity (without defect)

• Cost of EC devices

▫ 3X2 m2

▫ $500 /m2 [6]

▫ Material selection

▫ Deposition technique

Barriers to Implementation

6. Baetens, R. etal. (2010). Solar Energy Materials and Solar Cells, 94(2), 87-105.

• High optical contrast▫ Difference in the transparency in bleached and tinted states

• High colouring efficiency▫ Power requirement of the EC device

• Deposition technique

▫ Reagents

▫ Energy efficiency

▫ Time efficient

What makes a “Good” Electrochromic Window?

• Focusing on nano-structured metal oxides as they are the most common

• Tungsten trioxide (WO3) and nickel oxide (NiO) are the primary materials utilized

• Other materials:▫ Zinc oxide

▫ Titanium dioxide

▫ Indium tin oxide

Results of Literature Review

• Utilizing ultrasonic spray nozzle which atomizes the sol-gel solution

• The sol-gel solution forms nanoparticles on the substrate

• Li et al. [7] created WO3 thin films using USD

• Maximum transparency of 100%

• Optical Contrast = 70% after 1000 cycles

• Colouring Efficiency = 40 cm2

C

Ultrasonic Spray Deposition (USD)

7. Li, C. et al. (2015). Solar Energy Materials and Solar Cells, 132, 6-14.

Easy and Cost Effective Deposition

• Collective oscillation of free charger carrier electrons in response to incident electromagnetic radiation [2]

• Requires doped nanocrystals

• Causes absorption in the NIR range

• Can be tuned by adjusting doping levels

Local Surface Plasmon Resonance (LSPR)

[8]2. Granqvist, C. G. et al. (2010). Thin Solid Films,518(11), 3046-3053.8. Runnerstrom, E. L et al. (2014). Chemical Communications, 5(73), 1555-1572.

• A hierarchical porous ITO framework back filled with an electrolyte

• Williams et al. [9] crafted a device which has two states, ultra-violet (UV) selective and UV+IR selective

• The deposition process is rather complex

• Optical contrast = 8.3%

• Colouring efficiency = 501 cm2

C

Indium Tin Oxide (ITO) Framework

Infrared Red and Ultra-Violet

Selective

9. Williams, T. et al. (2014 Journal of Materials Chemistry c, 2(17), 3328-3335.

• Llordés et al. [10] combined ITO nanocrystals and POMs in solution and spin coated it onto a glass substrate

• Three stage device▫ Full transparent (red)

▫ NIR blocking (dark blue)

▫ VIS + NIR blocking (light blue)

• Did not investigate UV range

Nanocrystal-in-Glass Composite Three Stage

Device

10. Llordes, A. et al. (2013). Nature, 500(7462), 323-323.

• Electrochromic windows are energy efficient and increase user comfort

• Nano-structuring produces excellent EC films

• USD offers a facile inexpensive option

• The next generation of smart windows are already being researched▫ NIR-selective windows

• Much research is left to be done▫ Ageing and lifespan of device

▫ Consequences of scaling

▫ Complications of full device assembly

Conclusions

Thank you for your attention