Kijun Times

10808 So ye bin

Nowadays, the sun is being spotlighted since it’s a great energy source that is constantly radiating 7000 times as much energy that whole human use for a year as to Earth. To use the solar energy, we need solar cells that changes sunlight to electricity. Solar cells produce electricity by ‘photoelectric effect’ that makes voltage or current when matter is exposed to sunlight. However, the solar cells are not being used widely because of its price and efficiency, and the most hopeful technology to overcome this problem is using what is called ‘Perovskite’.

 Perovskite is a mineral composed of calcium, titanium, and oxygen. It is also a metal oxide that shows the characteristics of conductors, nonconductors, semi conductors, and even superconductors. Compared with silicon solar cells which are occupying 95% of existing solar cells market, perovskite solar cells are easy to produce and they cost only almost half of the silicon solar cells. Also, they become a light and thin battery with the form of film when we paint them like an ink, so we can bend them flexibly. Because of these features, we can emplace them on the curved place like a car’s roof. Recently, researches to enhance the solar cells’ efficiency using this matter are being proceeded actively, and one of the results is what is introduced below.

In this research, which is announced in march, by Eui Hyuk Jung and his team of Korea Research Institute of Chemical Technology(KRICT), researchers used ‘polymer poly’ (3-hexylthiophene)(P3HT) for transporting holes. The ‘hole’ is an imaginary particle that shows the lack of electrons in semiconductor. Though P3HT is cheap, appropriate for the solar cells, and has good productivity, the efficiency of the perovskite solar cells using P3HT has been under 20% until now. This is why this kind of limitation appears.

 Let’s think about a layer that perovskite block is sandwiched in the middle of it. In here, P3HT is located right under the perovskite block, The light absorbed by a perovskite block reaches the block and generates a pair of a negatively charged electron and a positively charged hole. Then, they are separated from each other and move to the different electrodes that are in the opposite side up and down, thereby generating a current. The problem is, that P3HT doesn’t make a good physical contact with perovskite. Also, because of the process called non-radiative recombination, separated electrons and holes can recombine at the perovskite–P3HT interface, resulting energy losses.

Then how did the researchers solve the problem? They overlaid the perovskite layer with a material, wide-bandgap halide (WBH), which hinders the current flows. When having overlaid the WBH on the perovskite layer, the recombination of the electrons and holes was decreased, and its stability was hugely increased to the others not using WBH. As a result, the research team could gain great efficiency of 22.7% in this research.

In addition, there have been many other achievements of KRICT about the perovskite solar cells. In last July, KRICT surpassed the efficiency of 19.7% recorded in 2017 in only one year, by developing a new hole transporting material called ‘DM’ and recording 20.9% of efficiency in a 1㎠ device, which is 10 times larger than the area of the unit device. Also, in this May, the same research team developed DHA(Double Layer Halide), a membrane technology with a new structure. The team formed it on the surface or the perovskite layer, achieving 24.23% of efficiency. The enhancement of solar cells like these is expected to contribute greatly for solving not only the world’s energy problem, but also global warming due to the use of fossil fuels.