High-performance Perovskite Opotoelectronic Devices Enabled by Additives
時 間：2019年7月2日（星期二）9:30 —11:30
報告人：Prof. Feng Gao (Linköping University）
Optoelectronic devices based on metal halide perovskites have developed very quickly during the past ten years. One of the important strategies to boost the performance is the employment of additives. In this talk, I will give two examples where the additives significantly improve the stability of perovskite solar cells and enhance the efficiency of perovskite light-emitting diodes (LEDs).
For perovskite solar cells, ion migration in the perovskite active layer, especially under light illumination and heat, is arguably the most difficult aspect to mitigate. We incorporate ionic liquids into the perovskite film, and demonstrate both a notable increase in efficiency and remarkable enhancement in long-term stability. We observe ~ 5% degradation of encapsulated devices under continuous simulated full-spectrum sunlight for over 1,800 hours at an elevated temperature of ~ 70 to 75 ˚C and estimate a T80 lifetime (time to 80% of its peak performance) of ~ 5,200 hours.
For perovskite LEDs, a major efficiency limit is trap-mediated non-radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures affect the passivation effectiveness. We reveal synergistic effect of precursor stoichiometry and interfacial reactions for perovskite LEDs. We show that hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring the perovskite, we significantly enhance the interaction with defects sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near infrared perovskite LEDs with a high external quantum efficiency (EQE) of 21.6%. In addition, our passivated perovskite LEDs maintain a high EQE of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm-2.
Dr. Feng Gao is currently an associate professor in the Department of Physics, Chemistry and Biology (IFM) at Linköping University. He obtained his Ph.D. in Cavendish Laboratory from University of Cambridge in 2011. And he received the ERC Starting Grant in 2016 and Wallenberg Academy Fellow in 2018. His research group currently focuses on the research into solution-processed energy materials and devices, mainly based on organic semiconductors and metal halide perovskites as well as lead-free halide perovskite materials and devices, including light-emitting diodes and solar cells. He has published over 100 papers in high-profile journals, including Science, Nature Materials, Nature Energy, Nature Photonics, Physical Review Letters, Advanced Materials, and Journal of the American Chemical Society, etc., with a total of citations of more than 5300 and an H-index of 32 as of today.