Magnetism and Magnetic Materials

Biography

Biography: Zhe Li

Abstract

As a next generation photovoltaic (PV) technology, solution processed organic solar cells have undergone significant improvements in their performance, now achieving the threshold for commercial viability. However, their environmental stability has been widely recognized as a major bottleneck for their commercialization. Various environmental factors including light, heat, oxygen and humidity, are known to cause rapid degradation of their performance, with the majority of their degradation mechanisms still remaining widely unclear. Such limitation has imposed further challenges in device encapsulation, which results in significant process limitations, higher costs and only partially effective process solutions. Organic solar cells are typically based upon solution processed conjugated donor polymers with the soluble fullerene derivative PCBM or its larger analogue PC₇₀BM. However, fullerenes are known to be expensive to fabricate and purify, and their weak optical absorption in the visible/near-infrared region and narrow range of available energy levels have limited further efficiency optimisation of organic solar cells. Recently, their highly sensitive nature to light and oxygen, as well as high tendency to nucleate and crystallize have been identified as primary degradation pathways of organic solar cells under various environmental stress conditions. Recently, the emergence of a range of non-fullerene acceptor materials has led further breakthroughs in the development of solution processed organic solar cells. Compared to their fullerene-based counterparts, these materials demonstrate great promise in achieving superior device performance with significantly reduced fabrication costs. Furthermore, while fullerenes are known to be linked with a number of major degradation mechanisms of organic solar cells particularly under light and thermal stress conditions, the use of non-fullerene acceptors instead of fullerenes represents a unique opportunity to address the stability challenge of organic solar cells. In this talk, author will combine a number of advanced characterization techniques to investigate the degradation of both fullerene-based and fullerene-free solution processed organic solar cells under various degradation environments especially under light, oxygen and thermal stress conditions, and demonstrate how a better understanding of the degradation mechanisms of their performance lead to improved materials and device design for improved solar cell stability, thereby significantly enhancing their commercialization potential of both types of organic solar cells.