A new type of PhotoVoltaChromic Cells (PVCCs)
A recent European directive has drawn the attention on the issue of energy efficiency in the building sector. In a nutshell, buildings need to be made less energy-consuming and more “active” towards the external environment. A number of ''smart'' have been implemented and tuned, capable of producing photovoltaic energy and screen solar radiations, to be integrated into the buildings' facades.
Photo-Volta-Chromic (PVCC) cells originate from the merging of a Dye Sensitized Solar Cell (DSCC), capable of producing photovoltaic energy, and an electrochromic device, who changes color as a function of the applied tension. As the solar light hits the PVCC device, the energy so produced can not only be stored, but it also generates the electrochromic effect, making the device self-sufficient in energetic terms.
The current architecture of PVCC devices does not allow splitting the photovoltaic functionality from the electrochromic one. For instance, if we imagine this system applied to a smart window, a stronger sunlight will make the window become darker. Until now, it was not possible to produce photovoltaic energy through a transparent window. Technically, this is because platinum, which is used as catalyser in DSSC cells, and tungsten oxide (an electrochromic material), must be laid on the same electrode.
The solution proposed by Francesco Malara, PhD at the National Nanotechnology Laboratory of CNR-NANO (Italy), allows the separation of the two functionalities. This is achieved by laying active materials on three different electrodes and by assembling them in a sort of “sandwich” configuration. The first electrode consists of a titanium oxide paste, laid on a conductive glass substrate. Through this architecture, it is possible to generate photovoltaic energy by simply varying the chromatic intensity of the window to one's taste.