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Energy-Harvesting Chromogenic Devices

Stage: Development
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 NREL have developed a thermochromic perovskite (e.g. CsPbI2Br) photovoltaic device that reversibly switches between a transparent and tinted state by a solid phase change. In its first state the device is transparent and converts only non-visible-spectrum light to electricity. When the device is sufficiently heated from sunlight, a phase change occurs and it absorbs the visible portion of the solar spectrum, thereby becoming tinted. This invention is a significant step toward the economical production of solar windows that dynamically modulate absorption and transmission properties while always converting incident sunlight into usable electricity.

This technology is within the Device Architecture category of NREL's perovskite portfolio. For further information regarding NREL's broader perovskite portfolio, please visit NREL's Perovskite Patent Portfolio website.

For more information on Energy-Harvesting Chromogenic Devices, please visit the Chromic Technologies for Photovoltaic Applications Portfolio Summary or contact Bill Hadley at Bill.Hadley@nrel.gov

ROI 17-09.

Applications and Industries

  • Smart windows
  • Building integrated photovoltaics
  • Commercial and residential buildings


  •  Switchable between light absorbing and transparent states
  •  Photovoltaically active in both absorbing and transparent state
  •  Tunable switching temperature