Scientists discover ideal material for smart windows that convert sunlight to electricity

Imagine a smart window that becomes transparent when it is dark or cool but darkens when the sun is bright, converting that sunlight into electricity.

Typical smart windows absorb or reflect sunlight without actually converting the solar energy into a useful form. However, the new photovoltaic windows would convert the sunlight on bright days into energy that provides more functional integration with buildings, automobiles, information displays and potentially many other technologies.

The research by Lawrence Livermore National Laboratory scientist Steven Hawks and colleagues from UC Berkeley, Lawrence Berkeley National Laboratory, Shanghai University, Purdue University and Stockholm University, appears in Nature Materials.

The team discovered that a form of perovskite, one of the newest materials in solar research due to its high power conversion efficiency, works surprisingly well as a reversible photoactive semiconductor material that can be switched between a transparent state and a non-transparent state, without degrading its electronic properties.

"We were looking to examine a reversible photoactive material that has large color contrast between states, one with high transparency to ensure the greatest brightness, and the other with strong light absorption to produce sufficient electrical energy." Hawks said. In addition, the two states can be reversibly switched back and forth in response to the external environment.

Previous research in this area used materials that cannot switch between a transparent phase and a nontransparent phase reversibly, without deteriorating their electronic properties.

The scientists made the discovery while investigating the phase transition of the material, an inorganic perovskite. When the material changes its crystal structure, it changes from transparent to non-transparent.

Metal halide perovskite materials are compounds with formula ABX3 that have the crystal structure of the mineral perovskite. Their unique properties, high photovoltaic efficiency and ease of processing have made it one of the most promising developments in solar technology in recent years.