"No Environmental or Farmland Damage"... Accelerating the Era of 'Urban Building Power Plants'

KIST Develops Efficient and Stable Building-Integrated Photovoltaic Materials

[Asia Economy Reporter Kim Bong-su] Current solar power generation faces challenges such as environmental destruction and farmland damage controversies. Another issue is that electricity is produced far from demand areas. As an alternative, technology for solar power generation on windows of urban buildings and houses is being researched. A domestic research team has developed building-integrated photovoltaic (BIPV) materials with excellent efficiency and stability, accelerating commercialization.

The Korea Institute of Science and Technology (KIST) announced on the 24th that the research team led by Center Director Jung Jeung-hyun and Dr. Yoo Hyung-geun at the Next-Generation Solar Cell Research Center, in collaboration with a research team from the State University of New York, developed a transparent solar cell technology using Cu(InGa)Se2 (hereafter CIGS) compound thin-film materials with outstanding power generation performance and long-term stability.

To achieve carbon neutrality by 2050, various alternative energy sources are being considered, with growing interest in solar power generation technology among them. However, South Korea, where population density is high and over 70% of the land area is mountainous, faces difficulties securing large-scale solar cell installation spaces. Therefore, building-integrated photovoltaic (BIPV) technology, which maximizes the use of existing urban buildings, is gaining attention. Window-type solar cell technology, a representative solar cell technology directly applicable to buildings, has been developed mainly using amorphous thin-film silicon, organic thin films, and dye-sensitized materials that allow partial light transmission to secure transparency, but efficiency and durability required for commercialization have not yet been achieved.

CIGS compound solar cells have high efficiency (23.4%) comparable to widely used crystalline silicon solar cells and high long-term stability, making them applicable in real life, but they are opaque. This is due to the material's high light absorption capability and the use of molybdenum metal as the electrode on the back of the solar cell, which is opaque and thus not transparent.

The research team applied a laser process capable of etching up to several micrometers (㎛) in size to increase the transmittance of the material's front surface. As a result, they were able to uniformly form fine patterns that allow light transmission by removing the opaque thin-film material at a size difficult to distinguish with the naked eye. The etched solar cells are transparent solar cells without a decrease in power generation performance and can be immediately used by replacing the glass currently used in building windows with solar cells or adding solar cells to existing glass.

To improve the efficiency of the laser etching process, it was necessary to apply transparent indium tin oxide (ITO) instead of the existing opaque molybdenum for the back electrode of the CIGS thin-film solar cell to allow laser irradiation through the back electrode. However, there was a problem of significantly reduced power generation performance due to the high electrical resistance at the ITO/CIGS interface. The research team confirmed that applying a 10 nm thick silver (Ag) precursor to the ITO back electrode could reduce the interface electrical resistance, developing technology capable of high-output power generation in a double-sided transparent CIGS thin-film solar cell structure. This cell structure allows not only front-side light power generation but also an additional 20-30% power generation from rear-side incident light, resulting in higher power output.

The developed transparent solar cell module allows free control of transmittance by adjusting the laser etching area ratio and has high power generation output (over 11% power generation efficiency at 30% light transmittance), enabling it to meet various transmittance demands required by buildings while producing more electricity. Additionally, the laser-etched light transmission pattern can be formed smaller than 100 ㎛, enabling aesthetically superior window production. By replacing conventional mechanical methods with precise laser etching during modularization, efficiency loss due to patterning was prevented.

Jung Jeung-hyun, KIST Center Director, stated, “The developed window-type solar cell is price-competitive and easy to commercialize because it utilizes already commercialized CIGS materials. We expect competitiveness to increase further by improving power generation performance and laser etching capabilities in the future.”

This research result was selected as the cover paper of the latest issue (July) of the international energy journal ‘Progress in Photovoltaics: Research and Applications.’

This content was produced with the assistance of AI translation services.