Dye-sensitized cells, which are transparent and flexible, overcome the limitations of conventional solar cells, open up a wide range of applications from personal mobile devices to buildings, and are being touted as a technology that will revolutionize the future energy market.
In the winter of 2013, a social media drama called “Infinite Power” aired on an internet video site in South Korea. The drama, which depicted the struggles and wanderings of young people facing the difficult realities of life in a boarding house, including job-seekers and high school students, was characterized by the “infinite power device,” which is also the title of the drama. The drama’s character, a boarding house owner, has long dreamed of creating an ‘infinite power device’. He collects scrap metal for his dream and researches it day and night, but others laugh at him for chasing an unattainable dream. As such, ‘perpetual motion’ was an unrealistic and impossible dream for humans. But what about a cell phone that never turns off no matter how much you use it? If it can be charged by the light from the liquid crystal when you use it, it can be said that it is a step closer to the long-standing dream of infinite power. Dye-sensitized solar cells (DSSCs), which are non-silicon-based solar cells, can make this kind of life a reality.
Dye-sensitized solar cells (DSSCs) look nothing like the solar cells we usually think of. Solar cells that generate power from the sun’s light or heat can be categorized into silicon and non-silicon types, and the solar cells we are most familiar with from electronic calculators and solar streetlights are silicon solar cells. Dye-sensitized solar cells belong to the non-silicon class of solar cells. Unlike conventional solar cells, non-silicon solar cells are based on inorganic or organic materials rather than polysilicon. Because they are made of organic dyes and a glass substrate, dye-sensitized solar cells have a novel appearance, like transparent glass.
How can this simple piece of glass become a cell? The principle of dye-sensitized solar cells is based on the principle of photosynthesis in plants, and the two processes are very similar. First, electron-hole pairs (excited electrons) are generated by sunlight on n-type nanoparticle semiconductor oxide electrodes with dye molecules chemically adsorbed on their surface. This is similar to the process of electron excitation by sunlight absorbed by chlorophyll during photosynthesis. The formed electron-hole pairs are injected into the conduction band of the semiconductor oxide and transferred across the nanoparticle interfaces to the transparent conductive membrane, generating a current. This is similar to the process of photosynthesis, where electrons travel through an electron transport system to generate energy. Finally, the holes created in the dye molecules are reduced back to electrons by an oxidation-reduction electrolyte, completing the operation of the dye-sensitized solar cell. This is reminiscent of the oxidation of water in photosynthesis, where electrons are taken away and holes are filled.
Using this principle, dye-sensitized solar cells can achieve transparent color properties because they use nano-sized oxides that can transmit some of the visible light and dyes that can represent different colors. Therefore, while conventional solar cells are opaque and used on rooftops, dye-sensitized solar cells can be used on glass windows and personal mobile devices because of their transparent color characteristics. In addition, the transparency of dye-sensitized solar cells is a major advantage because they can be used on both sides. Unlike conventional solar cells, they can be installed vertically and can be oriented both east and west. This allows them to generate power before sunrise and after sunset, and they can be oriented to the east or south with equal or greater power generation.
Dye-sensitized cells also have advantages in energy conversion efficiency. Previous studies have shown that when comparing silicon-based solar cells and dye-sensitized solar cells, dye-sensitized solar cells have higher energy conversion efficiency. In terms of energy conversion efficiency as the temperature of the cell changes, there was a smaller decrease in conversion efficiency as the temperature increased. In addition, the irradiation sensitivity also showed a smaller decrease in conversion efficiency as the sensitivity decreased compared to conventional cells. The change in conversion efficiency with the angle of irradiation was also smaller than that of conventional cells, which is why dye-sensitized cells stood out in terms of efficiency.
In April 2008, the original patent for dye-sensitized cells expired. Commercialization is currently being explored worldwide. The current solar market, which is centered on silicon-based solar cells, is expected to expand to non-silicon-based solar cells, which have many applications such as personal mobile devices and BIPV. Experts predict that this market will break even after 2023 and then grow rapidly. Cell phones that don’t need to be recharged, buildings that heat through glass, and other human imaginings are just around the corner.
