Lessons learned from 25 years of development of photoelectrochromic devices: A technical review

The energy performance of the building stock and the resulting emissions of greenhouse gases must be taken seriously into account for securing a sustainable future. Smart windows can transform a building to reach the standards of the Net Zero Emissions by 2050 Scenario. Among the currently available technologies, the Photoelectrochromic Devices (PECDs) promise extended functionalities beyond that of thermal and glare control, making them ideal for future buildings. PECDs use solar energy to generate and store electrical energy, simultaneously modulating their optical and thermal properties. A state-of-the art PECD can achieve a high optical modulation (<70%) and a photoconversion efficiency up to 7%, with switching times ranging from a few seconds to several minutes. In general, the performance of the devices is affected not only by the adopted materials properties, but also by the architecture of the devices. Therefore, they have a potential for remarkable energy savings in heating, cooling and electric lighting and are expected to play a significant role in the realization of energy efficient buildings. This review article summarizes the developments in the field of PECDs, since their first appearance ca. 25 years ago, giving emphasis on specific material properties and mechanisms that affect optical performance and solar energy harvesting.