PhD Oral Qualifying Examination : Plasmonic Semiconductor Nanocrystals for Spectrally-Selective Electrochromic Smart Windows

Speaker Zhang Shengliang (Supervisors: Prof Lee Jim Yang & Prof Adrain Fisher)

Host Department of Chemical and Biomolecular Engineering

Date/Time 12 Dec - 12 Dec, 4.00PM

Venue E5-02-32 , Faculty of Engineering, National University of Singapore

Synopsis

Dual-band electrochromic smart windows which support the dynamic and independent control of near-infrared (NIR) and visible (VIS) light transmittance can noticeably improve the building energy efficiency. Most of the dual-band electrochromic materials reported to date are composites of NIR-selective and VIS-selective components operating in different potential windows. Single-component materials with good dual-band performance are clearly desired but rare. Here, we report the discovery of a localized surface plasmon resonance (LSPR) and phase-transition assisted NIR modulation mechanism, which, together with the bandgap transition assisted VIS light electrochromism, enables the dynamic and independent control of NIR and VIS light transmittance by monoclinic oxygen-deficient tungsten oxide nanowires (m-WO3-x NWs), without the need for compositing with other electrochromic materials. The cast m-WO3-x NW films are able to operate in three distinct modes: the bright mode (4 V, NIR and VIS transparent), the cool mode (2.8-2.6 V, mostly NIR blocking) and the dark mode (2 V, NIR and VIS opaque). Of particular interest is the cool mode (at 2.6 V) where the m-WO3-x NW films can block 92.2% of the NIR to reduce the building solar heat gain, while maintaining a high VIS transmittance of 64.6% for daylighting. In addition, the cast films of m-WO3-x NWs also provide a high optical modulation of the full solar spectrum (91.7%, 92.7%, 94.6%, 87.3% at 633, 800, 1200, 1600 nm respectively), a high coloration efficiency (101.7 and 184.3 cm2 C-1 at 633 and 1200 nm respectively) and good cycle stability (8.3% of optical loss at 633 nm after 1000 cycles).

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