Electrochromic Inverse Opals for Smart Windows with Static and Dynamic Optical Transmittance

Christian LauMentors: Julia Greer and Victoria Chernow

Electrochromic Smart Windows

TiO2 + xLi+ + xe-

SageGlass Smart WindowSiemens Wind Turbine Facility. Hutchinson, Kansas

LixTiO2

Granqvist, Thin Solid Films, 2014

Visible and UV range

Near-IR range

Heat Transfer into Buildings

• 30-40% of energy consumption• Infrared light a significant source

of blackbody radiation

Spectra from the American Society for Testing and Materials

Spectral radiation on Earth’s surface

Incorporating Photonic Crystals into Smart Windows• Photonic Crystal:

“a low-loss periodic dielectric medium… with photonic bandgaps, preventing light from propagating in certain directions with specified frequencies” (Joannopoulos et al. 2008).

• Various methods reported for TiO2 inverse opal fabrication via sol-gel coating with tunable photonic bandgaps

Kim et al., Nature Asia Materials, 2011

Evaporative Self Assembly

Born et al., Langmuir, 2011

• Solvent evaporation at contact line causes convective flow into meniscus

• Capillary attraction between spheres causes aggregation

500 nm

Smart Window Design

+ + + + + + + + + + + + + + + + + + - -

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Transparent conducting oxide (ITO)

Soda Lime Glass

Electrolyte (LiClO4 in PC)

TiO2 Inverse Opals

Sealant Glue

• Static photonic bandgap in the near-IR• Dynamic electrochromism in the

visible range

Fabrication SchemeSubstrate Surface Modification

Evaporative Self Assembly of Opal Template

Calcination to Form Inverse Opal Arrayand Conversion of TiBALDH to TiO2

Hatton et al., PNAS, 2010 Lu et al., Nanoscale, 2014

Surface ModificationSoda-lime glass

Soda-lime glass

ITO

Effect of Surface ModificationITO

Soda-lime glass

OH OH OH OH OH

Superhydrophilic TiO2

Vertical Evaporative Deposition

Hatton et al., PNAS, 2010

Sol-Gel Composition: 0.14 mL 10% TiBALDH + trace EtOH + 1.0 mL polystyrene sphere stock solution (2.5 vol% in water) + 20 mL DI-Water

Vertical Evaporative Deposition• Curved regions of

meniscus deposit more uniformly than center region

Calcination/Baking Step

Lu et al., Nanoscale, 2014

• Heat sample to 400 ⁰C• Surface cracks widen at high

temperatures

400 ᵒC

400 ᵒC

Chemical Composition and Molecular Structure of Titania Inverse Opals

Literature raman spectrum taken from RRUFF database (RRUFFID: R070582)

Anatase TitaniaRutile Titania

Images by Kinsinger et al., Crystal Growth and Design, 2010

Conclusions• Factors affecting inverse opal fabrication• Substrate polarity• Deposition method (vertical deposition)• Cracking during baking

• Sol Gel methods are promising for fabricating titania inverse opal arrays with the optimal crystal phase

Future Work• Scalable doctor blade

coating of opal template• Device fabrication and

electrochemical tests

Yang and Jiang, Langmuir, 2010

Chen et al. ,ACS Nano, 2012

Acknowledgements• Vicitoria Chernow and Dr. Greer• Greer Group SURFs• Greer Group Grad Students• Student-Faculty Programs

Surface Modification: Titania Deposition

Soda-lime glass

ITO Ti layer

Treat with oxygen plasma and thermally oxidize Ti at 450 ᵒC Deposit 5nm layer of Ti by e-

beam evaporation

OH OH OH OH OH

Superhydrophilic TiO2