Abstract
An international team of researchers, affiliated with UNIST, has unveiled a novel cross-linker additives that significantly address the longstanding stability issues associated with organic solar cells, also known as organic photovoltaics (OPVs). With the incorporation of just 0.05% of this cross-linking agent, the lifespan of OPVs can be improved by over 59%. Industry analysts suggest this breakthrough brings the commercialization of OPVs-regarded as next-generation solar cells-closer to reality.
Led by Professor BongSoo Kim in the Department of Chemistry at UNIST, the research team, in collaboration with researchers from the University of California, Santa Barbara (UCSB), the University of Lille in France, and the French National Center for Scientific Research (CNRS), identified the operational principles of this innovative cross-linker using a variety of advanced analytical techniques.
OPVs are emerging as promising next-generation solar cells due to their ease of manufacturing and flexibility, allowing them to be applied as films. However, the inherent nature of organic materials poses challenges for long-term stability, particularly under heat exposure. While previous strategies have explored the addition of cross-linkers to enhance stability, excessive amounts often led to a decrease in battery efficiency.
The research team developed a 6-bridged azide cross-linker (6Bx), a highly efficient photo-crosslinker that demonstrates superior stabilizing effects with minimal additives quantities. As illustrated in Figure 1, 6Bx is composed of six azide cross-linkable units, which enables an impressive theoretical cross-linking efficiency of 96%. This efficiency significantly surpasses that of conventional cross-linkers, with four azide units yielding an efficiency of 82% (4Bx) and two azide units resulting in only 36% (2Bx).
Figure 1. (Top) Chemical structures of PM6, Y6, and 6Bx cross-linker. (Bottom) Power conversion efficiency (PCE) of OPVs fabricated with the new cross-linker.
The reported OPVs fabricated with the new cross-linker demonstrated an impressive efficiency of 11.70% even after 1,680 hours (70 days) at 85°C, retaining 93.4% of their initial efficiency. In contrast, OPVs produced without the cross-linker experienced a decline in efficiency to 8.17%, representing only 58.7% of the initial efficiency of 13.92%. This signifies a more than 59% improvement in performance longevity.
The research team also discovered that the elevated performance can be attributed to the effective suppression of molecular movement of the Y6 acceptor molecule in the photoactive layer of OPV devices, enabled by cross-linking reactions.
Professor Kim stated, "We have successfully addressed the chronic stability issues in organic solar cells through the development of high-efficiency photo-crosslinking agents and comprehensive investigations into their mechanisms." He further added, "This research will significantly contribute to the development of stability enhancement technologies for the commercialization of OPVs."
This study also involved contributions from Professor Thuc-Quyen Nguyen of UC Santa Barbara, as well as Professor G. N. Manjunatha Reddy from the University of Lille and CNRS in France. At UNIST, researchers Myongjae Lee and Seongju Yoo from the Department of Chemistry participated in the project. The research has been supported by the Samsung Future Technology Promotion Foundation, and the findings were published in ACS Energy Letters on January 10, 2025.
Journal Reference
Sangcheol YoonBraulio Reyes-SuárezSang T. Pham, et al., "Molecular Cross-Linking Enhances Stability of Non-Fullerene Acceptor Organic Photovoltaics," ACS Energy Lett., (2025).
