Withstanding Intense Sunlight... UNIST Improves Thermal Durability of Perovskite Solar Cells

Professor Kim Dong-seok's Team Optimizes Additive Ratios, Implements High-Temperature Stability Mechanism

Achieves 26.18% Photoconversion Efficiency and 85℃ Thermal Stability, Published in Joule Journal

The sun emits ‘light’ and ‘heat.’ While sunlight is converted into electrical energy through solar cells, solar heat actually accelerates the ‘aging’ of solar cells.

In particular, perovskite solar cells, the next-generation solar cells, are more vulnerable to heat. A research result that significantly improves the heat durability of these perovskite solar cells has been released, raising expectations for commercialization.

A research team led by Professor Dongseok Kim from the Carbon Neutrality Graduate School at UNIST (President Jongrae Park), in collaboration with Professor Taekyung Lee’s team at Gyeongsang National University and Professor Michael Gr?tzel’s team at ?cole Polytechnique F?d?rale de Lausanne (EPFL) in Switzerland, identified the cause that impairs the heat durability of perovskite solar cells and discovered an additive composition that enhances thermal stability while maintaining high efficiency. The findings were published on the 12th in the international journal Joule (IF: 38.6).

Professor Dongseok Kim's research team (top left). The center of the bottom row is Dr. Yunseop Shin, the first author. Provided by UNIST

Perovskite solar cells are considered next-generation solar cells because they use inexpensive materials and processing costs and can be printed in flexible film forms depending on the substrate.

For commercialization, they must withstand heat, humidity, and other factors while maintaining performance over a long period. Among these, improving heat durability was the final hurdle to commercialization. Humidity and other factors can be blocked by encapsulation technology that surrounds the cell, but heat durability requires improving the material itself, especially since the encapsulation process temperature can rise up to 100℃.

The research team fundamentally analyzed the factors that impair heat durability and found that the additive, which had been excessively added to improve cell efficiency, was the cause.

Based on the analysis, they reduced the content of 4-tert-butylpyridine (4-tert-butylpyridine, tBP) by more than 20 times, enabling the production of perovskite solar cells with high conductivity and efficiency while exhibiting excellent high-temperature stability. tBP is originally an additive used to improve the conductivity of the hole transport layer in perovskite cells. The hole transport layer is a material that transfers holes, charge carriers generated in the photoactive layer, to the electrode, and good conductivity is essential for improving solar cell efficiency.

According to the research results, a small amount of added tBP forms a 1:1 complex with another additive, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), improving conductivity by suppressing dedoping phenomena. Additionally, the glass transition temperature increased from the previous 77℃ to 105℃. The glass transition is a phenomenon where polymer materials become closer to a liquid state than a solid state, and the higher the glass transition temperature, the better the thermal stability.

This solar cell recorded a world-class photoelectric conversion efficiency of 26.18%, and achieved 23.29% efficiency even in a 25㎠ area module. It also demonstrated excellent stability through a durability test conducted at 85℃ for 1000 hours.

Dr. Yunseop Shin, the first author from UNIST, stated, “This research is significant as an innovative achievement that secured both high efficiency and high-temperature stability solely by optimizing the ratio of additives.”

Professor Dongseok Kim emphasized, “This study is like fitting the last puzzle piece for commercialization, as it developed technology that can withstand manufacturing processes above 100℃, along with long-term durability and high efficiency.”

Comparison results of the electrical properties of the Spiro-OMeTAD hole transport layer according to the change in dopant (additive) concentration. Photo by UNIST

This research involved Dr. Yunseop Shin and researcher Jiwon Song from UNIST, and integrated master’s and doctoral student Donggyu Lee from Gyeongsang National University as first authors. The research was supported by the Ministry of Science and ICT, the National Research Foundation of Korea (NRF), and the Ministry of Trade, Industry and Energy.

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