One of the problems with renewable energy is that the generators generally tend to take up a lot of space. Whether it is a solar farm or a wind farm, the area required to provide a decent amount of power is usually quite extensive. This is always inconvenient when areas that need the power most, such as cities, are almost always lacking in land to spare. We have all seen solar panels, and sometimes even wind generators on rooftops, and this does help, but in general the area of the roof only makes up a small amount of the total area of the building. Windows offer a better option for solar power generation as the amount of windows in modern buildings usually scale with the size of the construction, especially in larger buildings like skyscrapers which have thousands of windows.
Generating energy from windows is not a new idea. The model that offers the most potential currently is the Grätzel cell, a mesoscopic dye-sensitized solar (DSCs) cell, which was invented around a quarter of a century ago by Brian O'Regan and Michael Grätzel, who was a professor at École polytechnique fédérale de Lausanne (EPFL) and provides us with the name for the design. DSCs convert light into electricity through photosensitizers - dyes that absorb light and produce electrons that are collected by an array of oxide nanocrystals that allow electric current to be produced. DSCs are transparent and can be manufactured in multiple colours cheaply. While they are currently installed in some buildings, they tend to be quite inefficient, only generating small amounts of electricity. However, that could be changing, as scientists at EPFL have increased the power conversion efficiency of Grätzel cells to over 15% in direct sunlight and 30% in ambient light conditions.
The team used a technique called cosensitization, which produces DSCs with two or more different dyes that have complementary optical absorption. Using this method, it is possible to combine dyes that can absorb light from across the entire light spectrum, boosting the amount of power that can be collected. In addition, the researchers also developed a method of improving the packing of two newly designed photosensitizer dye molecules, which further enhances the DSC’s photovoltaic performance. Together, the new photosensitizers can harvest light across the entire visible domain. To pack the layers more tightly, a monolayer of a derivative of hydroxamic acid was pre-adsorbed on the surface of nanocrystalline mesoporous titanium dioxide to slow down the adsorption of the two sensitizers.
As a result of the new innovations, the team was able to develop DSCs with a power conversion efficiency of 15.2% under standard global simulated sunlight, with long-term operational stability tested over 500 hours. By increasing the active area to 2.8 cm2, a stable power conversion efficiency of between 28.4% – 30.2% was measured over a wide range of ambient light intensities along with outstanding stability. Hopefully the new way of making DSCs will bring us even closer to generating energy where it is needed.
