Ever heard of photovoltachromics, the new tech for solar windows?

Photovoltachromic devices (PVCDs) are capable of enabling adjustable transparency glazing and, at the same time, generate electricity by means of the PV effect. This technology has been so far applied to the design of self-powered smart windows for buildings and vehicles at research level and, however, it is still at a very early stage of development. The ability to modulate indoor light and heat transmission, while generating energy from PVs, is enticing for further BIPV developments.

Researchers in China have now taken a further step by developing a solar window based on a photovoltachromic device that combines a full-transparent perovskite photovoltaic device and electrochromic components based on ion-gel in a vertical tandem architecture without any intermediated electrode.

“This full-transparent monolithic smart window possesses not only full advantages of self-power, on-demand control and self-adaptive based on solar-irradiances, but also good features including excellent visible transparency and color neutrality, high adjustable range on transmittance and temperature, as well as repeatable serviceability,” the scientists stated

The Chinese group used visibly transparent perovskite and flexible electrochromic ion-gel to connect two terminals of PV element and two terminals of the electrochemical element in a four-terminal configuration. The perovskite layer was based on hybrid methylamine lead chloride (MAPbCl₃) perovskite film prepared by a spin coating method.

The monolithic PVCD device was assembled via a full solution process in an architecture incorporating glass, a fluorine-doped tin oxide (FTO) layer, the perovskite-based PV cell, the electrochromic gel, another FTO layer, and glass. This design, according to the researchers, offers the possibility of building large-area devices with a surface of approximately 36 cm². The electrochromic gel has a thickness of around  90 μm and the PV component of around 800 nm. The PV module consists of a 300 nm electron transport layer (ETL), a 350 nm perovskite layer, and a 40 nm hole-transport layer (HTL). When the PVCD is hit by sunlight, the PV module provides voltage to charge the electrochromic module.

“By optimizing the halide-diffusion period for perovskite, we successfully achieved a self-adaptable adjustment on transmittances depending on varying solar irradiation intensities for this monolithic PVCD,” the study reads. The PVCD is claimed to achieve a high pristine transmittance up to 76% and to be self-adaptable to control indoor brightness and temperature automatically depending on different solar irradiances.

A full description of the device can be found in the paper Full-frame and high-contrast smart windows from halide-exchanged perovskites, which was recently published in Nature Communications. The research group includes scientists from China’s Nanjing Tech University and the Nanjing University of Posts and Telecommunications.