Chromic materials can change their colors in response to heat (thermochromic) or voltage (electrochromic). Incorporation of these materials in smart windows enables the intelligent regulation of window transparency, allowing for control of transmitted light and heat into building interiors. This control allows improved energy efficiency and occupant comfort. With the application of heat or voltage, state-of-the-art chromic windows can switch from transparent to opaque and reject unwanted solar energy as heat. However, the National Renewable Energy Laboratory’s (NREL’s) chromic photovoltaic (PV) window technologies can transform a portion of the rejected or transmitted energy into electricity, using perovskite materials commonly found in PV panels of traditional architectures. To switch the transparency state of NREL’s chromic PV, heat or voltage trigger molecules to absorb into or desorb from the perovskite structure, causing a reversible change in bandgap properties.
Researchers at the National Renewable Energy Laboratory (NREL) have developed a tandem chromic window architecture with two photovoltaic absorber layers. The first absorber can be switched from transparent (resting) to opaque (photovoltaic) states. The first absorber layer can be made from, for example, metal halide perovskites switched by volatile molecules triggered by temperature or voltage as examples. The second absorber layer does not switch, is visibly transparent, and is always photovoltaic. The second layer can be made from organic or inorganic semiconductors. The absorbers are supported by a transparent layer like glass and placed atop each other or to the side and may be spatially separated or in contact with each other. A two- or four-terminal architecture may be used.
For further information regarding NREL's broader perovskite portfolio, please visit NREL's Perovskite Patent Portfolio website.
For more information on Photovoltaic Devices for Switchable Windows, please visit NREL's Chromic Technologies for Photovoltaic Applications Portfolio Summary or contact Bill Hadley at Bill.Hadley@nrel.gov.
Applications and Industries
- Smart windows
- Building-integrated photovoltaics
- Commercial and residential buildings
- Tandem layers provide enhanced conversion of light to electricity
- No chromic layer switching required for a photovoltaic effect