Lab Profile: Zhixiang Wei, National Center for Nanoscience and Technology, China

Organic nanomaterials hold promise for a new generation of photovoltaic devices, supercapacitors, lithium-ion batteries, and flexible sensors. Zhixiang Wei and his team at the National Center for Nanoscience and Technology in China are employing bottom-up approaches to assemble just such functional nanostructures and supramolecular structures with novel optical, electro-optical, and electrochemical properties. They are also developing printing methods to deposit these materials on flexible substrates to make bendy devices.

Zhixiang Wei received his BS and MS degrees from Xi’an Jiaotong University, before undertaking a PhD with the Institute of Chemistry, the Chinese Academy of Sciences. Following postdoctoral fellowships at the Max Planck Institute of Colloids and Interfaces in Germany and the University of Toronto in Canada, he returned to China as a professor at the National Center for Nanoscience and Technology. He received the Beijing Science and Technology Award in 2011, was named ‘youth chemist’ of the Chinese Chemical Society in 2009, and was given a Chinese Academy of Science President Award in 2003.

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

How long has your group been running?

The group has been run since January 2006, nearly 14 years up to now.

How many staff currently makes up your group?

There are currently about 30 people in my group.

What are the major themes of research in your group?

We are focused on the self-assembly of organic functional nanomaterials and flexible devices. We are developing self-assembly approaches for organic functional nanostructures by adjusting molecular structures and intermolecular interactions. We are especially interested in structures with chiral, electro-optical, and multifunctional properties. Further investigations on the potential applications are also being carried out in our lab, including photovoltaic devices, flexible sensors, supercapacitors, and lithium ion batteries.

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

I worked on the nanostructures of conducting polymers and oligomers when I did my PhD and during subsequent post-docs. When I joined the National Center for Nanoscience and Technology it was with the aim of developing better control of supramolecular structures, such as structures at different scales of chirality. From 2008 to 2010, we became interested in the potential application of these materials in flexible electronics. Therefore, we started studying flexible supercapacitors, lithium-ion batteries, and especially organic solar cells. We want to develop a better understanding and control of micro/nanostructures in flexible energy-related devices and, ultimately, translational technologies in this area.

What facilities and equipment does your lab have?

We have the facilities and equipment for chemical synthesis, self-assembly, and device fabrication. We have a chemistry lab, which enables us to synthesize new conjugated molecules. We also have an electrochemistry lab, where the assembly and characterization of flexible supercapacitors and lithium-ion batteries can be carried out. We have a cleanroom for organic solar cells, including a set of glove boxes for the fabrication of small-area devices and roll-to-roll slot-die printing facilities for flexible, large-area devices. We have grazing-incident X-ray scattering for characterizing the morphologies of materials, as well facilities for power conversion efficiency and external quantum efficiency measurements.

Do you have a favorite piece of kit or equipment?

All equipment is important to carry out our research, but my personal favorite is our grazing-incident X-ray scattering instruments, which not only serve our group but also help various other groups in the characterization of organic solar cell morphology.

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

The ability to control the micro-/nanostrucuture is of great importance for the performance of organic functional materials and devices. In this field, I think two pieces of our work have been important.

Firstly, transferring molecular chirality to supramolecular chirality at nano- and microscales by chemical self-assembly has been studied intensively. We have shown the ability to control the chirality of conducting polymers in nano- and macrostructures by using enantiomers of dopants. Recently, we have revealed how the chirality from molecular level transfers to macroscopic level via self-assembly (Figure 1). A multiscale chemo-mechanical model elucidates the mechanism underlying chirality induction in this ribbon. This study indicates a class of general chiral induction behavior in both natural and artificial hierarchical ordered structures, which is important for the production of chiral materials at all scales.

Secondly, controlling the morphology of bulk heterojunction structures is important for organic solar cells. Ternary blends have the potential to optimize the morphology and broaden the absorption. However, improving the power conversion efficiency is quite challenging for ternary systems because of the complexity of phase separation behavior. We have introduced a ternary organic solar cell including two donors (one is a polymer and the other is a small molecule) and one accepter (PC₇₁BM). We propose the two donors form an alloy in the ternary blend (Figure 2). This ternary strategy is becoming a popular means of improving the efficiency of organic solar cells, and we reported the first ternary organic solar cells with PCE greater than 10%. Up to now, our ternary strategy has become a general method for improving the performance of organic solar cells.

What is the key to running a successful group?

I think the self-motivation of students is the most important thing. To achieve this, discussion about progress and experimental details is always helpful.

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

I plan to continue the study of the self-assembly of organic functional nanomaterials and flexible devices. First, we need better control of self-assembly, especially for complicated systems. Secondly, we need to improve the performance of various flexible devices. Thirdly, efficient integration design will be important for the application of organic functional nanomaterials and flexible devices.

Key publications

1. G.D. Wang, M. A. Adil, J. Q. Zhang, Z. X. Wei. Large-Area Organic Solar Cells: Material Requirements, Modular Designs, and Printing Methods. Adv. Mater. 31, (2019) 1805089. https://doi.org/10.1002/adma.201805089

2. Q. Wu, D. Deng, J. Q. Zhang, W. J. Zou, Y. Yang, Z. Wang, H. Li, R. M. Zhou, K. Lu, Z. X. Wei. Fluorination-substitution effect on all-small-molecule organic solar cells. Sci. China Chem. 62 (2019) 837-844. https://doi.org/10.1007/s11426-018-9437-7

3. Y. Yang, J. Liang, F. Pan, Z. Wang, J. Q. Zhang, K. Amin, J. Fang, W. J. Zou, Y. L. Chen, X. H. Shi, and Z. X. Wei. Macroscopic helical chirality and self-motion of hierarchical self-assemblies induced by enantiomeric small molecules. Nature Commun. 9 (2018) 3808. https://doi.org/10.1038/s41467-018-06239-5

4. Z. Wang, X. W. Zhu, J. Q. Zhang, K. Lu, J. Fang, Y. J. Zhang, Z. Y. Wang, L. Y. Zhu, W. Ma, Z. G. Shuai, Z. X. Wei. From Alloy-Like to Cascade Blended Structure: Designing High-Performance All-Small-Molecule Ternary Solar Cells. J. Am. Chem. Soc. 140 (2018) 1549-1556. https://doi.org/10.1021/jacs.7b13054

5. K. Amin, Q. H. Meng, A. Ahmad, M. Cheng, M. Zhang, L. J.Mao, K. Lu, Z. X. Wei. A Carbonyl Compound-Based Flexible Cathode with Superior Rate Performance and Cyclic Stability for Flexible Lithium-Ion Batteries. Adv. Mater. 30 (2018) 1703868. https://doi.org/10.1002/adma.201703868

6. 6. L. Yuan, K. Lu, B. Z. Xia, J. Q. Zhang, Z. Wang, Z. Y Wang, D. Deng, J. Fang, L.Y. Zhu, Z. X. Wei. Acceptor End-Capped Oligomeric Conjugated Molecules with Broadened Absorption and Enhanced Extinction Coefficients for High-Efficiency Organic Solar Cells. Adv. Mater. 28 (2016) 5980-5985. https://doi.org/10.1002/adma.201600512

7. D. Deng, Y. J. Zhang, J.Q. Zhang, Z.Y. Wang, L.Y. Zhu, J. Fang, B. Z. Xia, Z. Wang, K. Lu, W. Ma, Z. X. Wei. Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells. Nature Commun. 7 (2016) 13740. https://doi.org/10.1038/ncomms13740