The Korea Institute of Materials Science (KIMS, President Lee Jeong-hwan), a government-funded research institute under the Ministry of Science and ICT, has developed a flexible substrate transparent thin-film solar cell that can express various colors at once at low cost and high efficiency. Expectations are high that it will be used in various industries with high aesthetic value, such as building-integrated solar power and vehicle-integrated solar power in the future.

The Korea Materials Research Institute announced on the 21st that the research team led by Dr. Jeong-Dae Kwon of the Energy and Electronic Materials Laboratory has succeeded in developing the world's first flexible substrate transparent thin-film solar cell that exhibits various reflection colors without significantly reducing solar cell efficiency.

This study is a technology that implements a reflective color using only a single material by periodically mixing hydrogen into a zinc oxide material doped with aluminum, which is a transparent electrode, to induce a difference in refractive index.

By designing a multilayer thin film with an extremely low refractive index difference of less than 5%, reflection loss in the visible light range absorbed by the solar cell element was minimized.

Because the color implementation hardly reduces solar cell efficiency, it can be applied to various absorbers for thin-film solar cells.

It is also expected to serve as a benchmark for improving the aesthetics of flexible substrate transparent thin-film solar cells for BIPV (Building Integrated Photo Voltaic) and VIPV (Vehicle Integrated Photo Voltaic).

Until now, color application methods for improving the aesthetics of transparent thin-film solar cells have included multilayer thin-film technology using materials with large refractive index differences, color-controlled thin-film layer technology for optical characteristic design, and structural color technology imitating natural structures.

On the other hand, these The technology is not suitable for solar cells that absorb visible light due to its wide reflection band and high reflectivity, or it requires a complex technology that is difficult to apply industrially due to the use of two or more materials and processes.

The research team deposited a zinc oxide thin film using a vacuum sputtering deposition method used in general semiconductor and solar cell manufacturing processes, and formed a multilayer thin film with different refractive indices through periodic hydrogen reactions.

Afterwards, the thickness of the multilayer film was adjusted to obtain the three primary colors of light. The colors of the electrodes were successfully applied to solar cells that absorb light in the visible light range.

A multilayer thin film transparent electrode based on a single material does not require additional processes. It is expected that it will be possible to implement various colors and high efficiency of thin-film solar cells at low cost.

Additionally, since the reflective color is implemented as a light filter, it is expected to be applicable to various fields such as image sensors, photolithography masks, and infrared shielding that require it.

Kwon Jeong-dae, a senior researcher at the Materials Research Institute, said, “If this technology is commercialized, it is expected to be of great help in the development of simple, process-friendly optical filter technology and high-efficiency colored flexible substrate transparent thin-film solar cells, as well as in the realization of BIPV systems for modern buildings and VIPV systems for vehicles that take aesthetic characteristics into account.”

This research was conducted through the basic project of the Korea Institute of Materials Science and Technology and the energy technology development project of the Korea Institute of Energy Technology Evaluation and Planning with support from the Ministry of Science and ICT.

In addition, the research results were published on August 3 in the Chemical Engineering Journal (IF: 15.1), a top-tier journal in the field of chemical engineering (within the top 3%) (first author: Dr. Soo-Won Choi, co-corresponding author: Professor Poong-Geun Song of Pusan National University, Professor Myeong-Hoon Shin of Korea Aerospace University).

Based on this study, the research team is actively conducting follow-up research in the field of solar modules that express colors that take into account both the aesthetic and practical aspects of BIPV.