Semitransparent Perovskite Solar Cells for Smart Windows

摘要： Smart windows, whose transparency can be tuned dynamically and even reversibly changed from transparent to opaque, have been the focus of research since the 1970s [1]. For one thing, smart windows can control the transmission of sunlight into the building, achieving energy savings by balancing the cooling load with the energy requirements of lighting and heating. For another, opaque glass walls act like curtains to protect privacy. The existence of smart windows reduces dependence on manual intervention, and motivates people's lives to become intelligent. The electrochromic windows, whose color can be reversibly changed by applying a small external electric field, have been investigated for use on Boeing 787 Dreamliner airplane [2]. The electrochromic windows are undoubtedly effective, but lack of advantages in inconsistent light-shielding, long-term non-durability and high cost. Thermochromic windows, whose color can be switched by the application of local temperature, have been also investigated. However, such technologies have limitations in impractical high-temperature heating conditions and relatively low light-dark contrast. Besides, the above-mentioned smart windows require external source of energy, thereby failing to achieve the purpose of saving energy. If the photoelectric conversion of solar cells and intelligent control of light transmission are tactfully combined in smart windows, the situation will be changed qualitatively [3]. To date, semitransparent photovoltaics have been proven to be used in power generation windows that provide power output, shading and even heat insulation effect [4, 5], but rarely referring to color switch characteristics. Therefore, it is highly desirable to integrate both functions composed of color-adjustment and power-generation to develop semitransparent photovoltaics as smart windows.