Llordés et al. at Lawrence Berkeley National Laboratory (USA) have reported these days in Nature an outstandng electrochromic device capable to block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. This material demonstrates a novel optical
switching behaviour that will enable the dynamic control of solar
radiation through windows.
The change in transmittance is achieved at different voltages applied to the device (left graph). The right picture shows the device at fully transparent state (pictures from Nature).
They achieve this by incorporating tin-doped indium oxide (ITO) nanocrystals into niobium oxide glass. This synthetic strategy is called "nanocrystal-in-glass" and nanocrystals become covalently bonded into the amorphous material, resulting in a new amorphous structure. The nanocrystal-in-glass film switches progressively between three optical states:
- Fully transparent (at 4V versus Li)
- Selective blocking of near-infrared (around 2.3 V)
- Simultaneous blocking of visible and near-infrared (1.5 V)
Thus, solar radiation can now be dynamically modulated with spectral selectivity. For example, we can select reducing the infrared part during hot days (reducing the air conditioning consumption). Both infrared and visible can be cut down in very hot days to gain also privacy and reduce heat input further, or we can also leave it transparent during the winter. Additionally the new material is also highly stable to swith on/off cycling.
