Solar cells are a technology that converts the sun’s abundant energy into electricity, and color-sensitive solar cells, in particular, boast high energy conversion efficiency by applying the principle of photosynthesis in plants, and are expected to play an important role as a clean energy source in the future.
On a sunny day, under a clear sky, we often feel the warmth of the sun. However, this warmth is not just a pleasant heat, but a tremendous energy source when analyzed scientifically. The amount of energy that the sun shines on the Earth’s surface in a single day is staggering, and the ability to harness it efficiently is one of the major challenges of modern science. The sun’s light provides about one kilowatt of energy per square meter. Finding ways to effectively harness this abundance of solar energy is a major challenge for humanity. Solar cells are devices developed to convert this abundant and almost permanent solar energy into electricity.
Currently, silicon solar cells are used primarily in satellites and expensive devices because their main material, silicon, is very expensive to process. This is due to the high purity of silicon and the precise processing required, so new solar cell technologies are being researched as a cost-effective alternative. This research is not just about reducing the cost of the cells, but involves different approaches to maximize their energy conversion efficiency. This has led to the development of solar cells using titanium oxide as a photocatalyst, which is readily available and inexpensive to manufacture, but it has the disadvantage that the wavelengths of light that can be used to generate electricity are in the ultraviolet range, below about 400 nanometers. This ultraviolet light is very small, only about 4-5% of the sunlight that reaches Earth. To overcome this disadvantage, tintable solar cells were developed by applying the principle of artificial photosynthesis.
Artificial photosynthesis is a technology that mimics the complex and sophisticated energy conversion process that occurs in nature, and is an adaptation of the way plants harness sunlight to produce energy. Plants utilize nearly 100% of the energy in sunlight to create and use the energy they need, and artificial photosynthesis was developed to mimic this sophisticated system to increase the efficiency of energy conversion. While plants use water and carbon dioxide to produce organic matter and oxygen in this process, artificial photosynthesis technologies are primarily focused on converting solar energy into electricity or breaking down water to produce hydrogen. These technologies are expected to play an important role in the production of hydrogen, the clean energy resource of the future, beyond simply generating electricity.
When plants absorb sunlight to create energy, pigments such as chlorophyll play an important role in absorbing solar energy. Pigment-sensitized solar cells mimic this principle of photosynthesis, allowing more sunlight to be used for power generation by adsorbing photosensitive dyes (pigments) onto titanium oxide thin films that can easily pick up electrons in the visible light region with a wavelength of 500 to 600 nanometers. The electrons from the light-excited dye are injected into the conduction band of the titanium oxide, and as they move from the cathode to the anode, a current flows, and the dye that has released its electrons returns to its electrically neutral state through a redox reaction with iodine (I) in the electrolyte solution, generating electricity. The cells use microscopic particles of titanium oxide with a diameter of 10 to 30 nanometers as electrodes, which are micromachined to increase the surface area of the titanium oxide as much as possible so that as much pigment as possible can be attached to them.
The energy conversion efficiency of the color-sensitized solar cell is much higher than previous solar cells, with studies showing that it can convert more than 50% of the light energy collected by the pigment molecules into electricity. In addition, hydrogen, which is beginning to gain attention as a clean energy source, can be produced much more economically than in the past by using photocatalysts to decompose water to obtain oxygen and hydrogen, which is much more efficient than the method of using electricity from sunlight to decompose water again to obtain hydrogen. Advances in these technologies are expected to dramatically change the way energy is produced in the future and make an important contribution to the development of sustainable energy resources. In addition, it is easy to make transparent thin films that allow light to pass through, and recently, cells using PET film as a substrate have been developed, which is expected to be utilized in more diverse ways. This will open up the possibility that solar cells can be more easily applied in future buildings and electronic devices.
