Lab profile: Wallace C. H. Choy, The University of Hong Kong

In the future, flexible displays, lighting, solar cells, and other types of optoelectronic devices could roll off the presses like paper. But such novel and cost-effective technologies require understanding of the physics and optical/electronic/thermal properties of hybrid organic/inorganic materials.

Wallace C. H. Choy has always had a strong interest in the field, since receiving his PhD in electronic engineering from the University of Surrey in the UK. He subsequently moved to the National Research Council of Canada as a researcher and then Fujitsu in San Jose, USA. Currently, Choy is a professor in the Department of Electrical and Electronic Engineering, the University of Hong Kong (HKU), where he leads a research group focused on organic/inorganic nanoscale optoelectronics. He has received the Sir Edward Youde Memorial Fellowship, the Croucher Foundation Fellowship, the Outstanding Achievement Award from National Research Council of Canada, and HKU Research Output Prize. He is also a fellow of OSA and senior member of IEEE.

Wallace talked to Materials Today about his current research and future plans.

How long has your group been running?

My group has been running for 17 years.

How many staff currently makes up your group?

My group current has 20 PhD students, four postdocs, and one visiting scientist.

What are the major themes of research in your group?

Our major themes of research are interface materials and engineering, organic and inorganic materials, and optoelectronics.

How and why did you come to work in these areas?

Optoelectronics technologies (e.g. displays and lighting, photovoltaics, and imaging technologies) have been continuously evolving to improve our quality of life and have indeed become part of daily life. With my strong interest in the field, I received rigorous training at universities, national labs, and industries on different aspects of optoelectronic materials, right through to modules. Currently, our group aims to advance organic and inorganic materials, as well as interface materials and engineering, through simple, low cost, scalable approaches to develop new kinds of optoelectronic devices.

What facilities and equipment does your lab have?

Besides sharing central facilities for large equipment including X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM), our labs are equipped with inert-environment facilities for fabricating organic/inorganic/metal hybrid material systems and structural devices, as well as investigating optical-electrical-thermal properties of hybrid structure optoelectronic materials and devices.

Do you have a favorite piece of kit or equipment?

Generally, we have made close friends with the equipment enabling hybrid structure formation and characterization.

What do you think has been your most influential work to date?

We have made extensive experimental and theoretical contributions on hybrid materials and structures in the fields of plasmonics, optoelectronics, and photovoltaics. We have performed original research work addressing the challenging issues of light trapping, carrier generation, and carrier extraction in photovoltaics. Notable among this work are new concepts and multi-physical understanding of plasmo-electrical effects of hybrid structures on photovoltaics. We have extended our work to demonstrate a universal approach based on metal-oxide based nanomaterials for enabling hybrid systems with enhanced the optical and electronic properties for new applications. To realize practical optoelectronics, we are proposing novel nanostructure-oriented approaches for improving crystallization and passivation of photoactive hybrid materials. Meanwhile, some of our materials and approaches are now being studied and potentially adopted by stock-listed companies developing practical devices.

What is the key to running a successful group?

We are dedicated to exploring important issues in the field and our team is committed to address them together. We do our best to be supportive of and motivate all team members, to stimulate each other in creative thinking about projects and explore collaboration to develop new findings.

How do you plan to develop your group in the future?

We will continue our commitment to address high impact problems in these fields, particularly new classes of low-cost and scalable hybrid materials and structures, while developing fundamental understanding of emerging optoelectronics such as flexible electronics, photovoltaics, and imaging.

Key publications

1. H. Zhang, X. Ren, X. Chen, J. Mao, J. Cheng, Y. Zhao, Y. Liu, J. Milic, W.J. Yin, M. Grätzel, W.C.H. Choy. Improving the stability and performance of perovskite solar cells via off-the-shelf post-device ligand treatment. Energy Environ. Sci. 11 (2018) 2253-2262. https://doi.org/10.1039/C8EE00580J
2. H. Zhang, J. Cheng, D. Li, F. Lin, J. Mao, C. Liang, A. K.-Y. Jen, M. Grätzel, W.C.H. Choy. Toward All Room-Temperature, Solution-Processed, High-Performance Planar Perovskite Solar Cells: A New Scheme of Pyridine-Promoted Perovskite Formation. Adv. Mater. 29 (2017) 1604695. https://doi.org/10.1002/adma.201604695
3. F. Jiang, W.C.H. Choy, X. Li, D. Zhang, J. Cheng. Post-Treatment-Free Solution Processed Non-Stoichiometric NiO_x Nanoparticles for Efficient Hole Transport Layers of Organic Optoelectronic Devices. Adv. Mater. 27, (2015) 2930–2937. https://doi.org/10.1002/adma.201405391
4. X.C. Li, F.X. Xie, S.Q. Zhang, J.H. Hou, W.C.H. Choy. MoO_x and V₂O_x as Hole and Electron Transport Layers through Functionalized Intercalation in Normal and Inverted Organic Optoelectronic Devices. Light: Sci. & Applications 4 (2015) e273. https://doi.org/10.1038/lsa.2015.46
5. F.X. Xie, W.C.H. Choy, W.E.I. Sha, D. Zhang, S. Zhang, X. Li, C.W. Leung, J. Hou. Enhanced Charge Extraction in Organic Solar Cells through Electron Accumulation Effects Induced by Metal Nanoparticles. Energy Environ. Sci. 6, (2013) 3372 – 3379. https://doi.org/10.1039/C3EE42440E
6. X.H. Li, W. C.H. Choy, L Huo, F.X. Xie, W.E.I. Sha, B. Ding, X. Guo, Y. Li, J. Hou, J. You, Y. Yang. Dual Plasmonic Nanostructures for High Performance Inverted Organic Solar Cells. Adv. Mater. 24 (2012) 3046-3052. https://doi.org/10.1002/adma.201200120