Speaker: Wallace C. H. Choy

Time and Date: 09:30 am, December 23, 2019

Place: Room 301 of Electric Light Source Building, Handan Campus, Fudan University

Abstract:

  We demonstrate that effective solution-based approaches to control the composition, morphology, and thus the quality of the perovskite films. With our theoretical prediction and understanding of the theoretical limit and electrical and optical properties of perovskite solar cells [1], we will firstly show that the vacuum-assisted thermal annealing can be used as an effective approach to control the composition, morphology, and thus the quality of the perovskite films formed from the precursors of PbCl₂ and CH₃NH₃I for achieving high power conversion efficiency (PCE) perovskite solar cells. Remarkably, the complete elimination of CH₃NH₃Cl not only considerably improves the stability and reproducibility of the perovskite device (standard deviation in PCE of only 0.92% was achieved for 60 solar cells) [2]. By forming intermediate adducts at low temperature [3], we will report new room temperature solution-processed perovskite solar cells (PVSCs) with the features of PbI₂ residue-free, large grain-sizes, and highly crystalline. Using our approach, the PVSC with no hysteresis, high power conversion efficiency of about 18% which is the best of the perovskite solar cells fabricated by low-temperature techniques to date [4]. In addition, using the formation of intermediate adducts, we can form perovskite nanograting patterns with simultaneously enhancement of crystallization and optical absorption [5, 6]. We have also newly demonstrated a post-device ligand treatment to simultaneously improve the performance and air stability of perovskite solar cells as well as repairing the ‘poor device’ for the first time. The enhancement of power conversion efficiency can be over 900% [7]. Regarding hole transport layer (HTL), NiO_x is a promising material for candidate for fabricating efficient PVSCs, the reported NiO_x HTLs are formed using different multi-step treatments, which hindering its applications in PVSCs. Here, we demonstrate the flawless and surface-nanostructured NiO_x nanoparticle film [8] from a simple and controllable room-temperature solution process [9]. We have also been working on ternary oxide such as NiCoO_x functioning as effective HTL [10]. Recently, we have demonstrated stable and high performance solar cells with no hysteresis and PCE of 21.5%. The work contributes to the large-sale and low-cost production of perovskite solar cells with high device performances.

Biography:

  Wallace Choy received Ph.D Degree in Electronic Engineering from University of Surrey, UK in 1999. After vigorous working experiences in National Research Council of Canada and Fujitsu at San Jose, on investigating optoelectronic devices, he is now a professor of Department of Electrical and Electronic Engineering, the University of Hong Kong. His current research interests are concerned with organic/inorganic optoelectronic devices, plasmonic structures, and nano-material devices and physics. Prof. Choy is named as one of the "Highly Cited Researchers" in the category of cross-fields in 2018. He has also been recognized as the Top 1% of most-cited scientists in Thomson Reuter's Essential Science Indicators (ESI) in 2014, 2015, 2016, 2017 and 2018. He has been named as prolific researcher on organic solar cells in the index (WFC in physical sciences) in Nature Index 2014 Hong Kong published by Nature. He has published about 200 internationally peer-reviewed journal papers, contributed to seven book chapters, US and China patents and edited one book published in Springer. He has served as Member of Engineering panels of Hong Kong Research Grant Council, Editorial Board Member for Nature Publishing Group on Scientific Reports, Wiley on Solar RRL and Institute of Physics on J Physics D, senior editor of IEEE Photonics Journal, topical editor of OSA Journal of the Optical Society of America B, and guest editor of OSA Journal of Photonic Research, and Journal of Optical Quantum Electronics. He is an elected fellow of OSA.