A research team led by Dr. Jung-dae Kwon from the Department of Energy & Electronic Materials at the Korea Institute of Materials Science(KIMS) has succeeded in realizing the world's first transparent thin-film solar cell on a flexible substrate that exhibits different reflective colours and does not significantly reduce solar cell's efficiency. KIMS is a government-funded research institute under the Ministry of Science and ICT.
This is a technology that achieves reflective colour only a single material by periodically incorporating hydrogen into zinc oxide material doped with aluminium, which is a transparent electrode, to induce a refractive index difference. By designing a multi-layer thin film with an extremely low refractive index difference of less than 5%, the reflection loss in the visible light region absorbed by the solar cell device was minimized. It can be applied to various absorbers for thin-film solar cells as it hardly reduces the solar cell efficiency due to colour implementation. In addition, it is 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).
To date, multilayer thinning technology for materials with large refractive index differences, colour control thin film coating technology for designing optical properties, and natural structure mimicking structural colour technology have been used as colour application methods to improve the aesthetics of transparent thin film solar cells. However, these technologies are not suitable for solar cells that absorb visible light due to a wide reflection band and high reflectivity or require complex technologies that are difficult to apply industrially in terms of two or more materials and processes.
The research team formed multilayer thin films with different refractive indices through periodic hydrogen reactions while depositing zinc oxide thin films using the vacuum sputtering deposition method used in general semiconductor and solar cell manufacturing processes. They then obtained the three primary colours of light by adjusting the thickness of the multilayer thin film. At that time, the colour of the electrode was well implemented even when applied to a solar cell that absorbs light in the visible light range.
Multilayer transparent thin film electrode based on a single material does not require additional processing. It is expected that various colours and high efficiency of thin film solar cells can be realized at a low cost. In addition, since the reflective colour is implemented as an optical filter, it can be applied to various fields such as image sensors, photolithography masks, and infrared shielding.
Dr. Jung-dae Kwon, a principal researcher, said,"When commercialized, this technology will help to develop simple and process-free light filter technology and high-efficiency coloured flexible substrate transparent thin-film solar cells, as well as to realize BIPV systems for modern buildings and VIPV systems for vehicles with aesthetic features."
This research was carried out under the basic research project of the Korea Institute of Materials Science 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 3 August in the Chemical Engineering Journal (IF: 15.1), a top-tier journal (in the top 3%) in the field of chemical engineering (First Author: Dr. Choi Soo-won, Corresponding author: Pusan National University, Professor Punggeun Song, Korea Aerospace University, Professor Myung Hoon Shin). Based on this research, the research team is actively conducting follow-up research in the field of solar modules that express colours considering both the aesthetic and practical aspects of BIPV.