Electrically switchable window technology typically includes Electrochromic (EC), Polymer Dispersed Liquid Crystal (PDLC), and Suspended particle device (SPD).
The above figure schematically shows the device structure and operating principle of a SPD.
The characteristic of a SPD:
- Active layer: optically absorbing particles suspended in a cross-linked polymer matrix; The particles are:
- Needle-shaped dipolar particles with large optical anisotropy
- Material examples: poly iodides (polyhalide crystals), e.g. iodoquinine sulfate or herapathite
- Particle size: less than 200 nm to minimize scattering and haze
- ITO layer can be the conductive layer
- Advantages:
- Short switching time: 1-3 seconds
- Dark blue color, good for automobile applications
- Remain dark state when power off; AC powered
- Disadvantages:
- High voltage requirement to obtain transparent state
- Low transparency and high haze at clear state
- No control over NIR
- Low temperatures tend to give slow switching