(6do) Advanced Materials and Nanotechnologies for Efficient, Solution Processable Energy Devices

In the past century, the extent to which discoveries of new molecules and materials have impacted technology, particularly in the energy sector, has been dramatic. These materials have quietly transformed the way we live, finding their way into chemical production, energy production, transportation, and information technologies. However, as the world energy consumption continues to grow, we are still mainly replying on limit resources such as petroleum for energy generation. How to meet the ever-increasing energy consumption in a sustainable way is extremely important and challenging for human society’s long term development.

My main interests lie in exploring and developing next generation materials (from 3D to 0D crystal structures, and from bulk materials to nano-structures) with an emphasis on their potential applications especially in energy harvesting (Photo-energy and thermal energy to electricity), electronic and optoelectronic devices, as well as energy storage using cost and energy efficient solution processes. I aim to 1) design and synthesize multifunctional materials with low dimensional crystal structures; 2) investigate the fundamental properties of these materials; 3) develop high performance energy harvesting devices as wellas other electronic and optoelectronic devices and 4) incorporate flexibility, stretchability, and transparency into high performance thin film devices for ubiquitous electronics.

During my postdoctoral research, I have successfully explored several material systems for photovoltaic and optoelectronic devices. One of such material systems is environmental friendly organic-inorganic hybrid perovskite materials for photo-energy harvesting. The sun is continuously supplying us with photo-energy that is freely available by nature, but harvesting the photo-energy efficiently and cost-effectively is challenging at present due to the high processing cost, complex processing steps and material recycling. I have designed a universal processing protocol for synthesizing Sn-based halide perovskites that have a great potential to achieve over 30% efficiency for PV theoretically. Through molecular precursor design, I successfully achieved over 5 times improvement on the solar cell performances. I have also explored these materials’ potential application in X-ray detectors and thermoelectric devices. Furthermore, I have designed and built an integrated in-situ characterization system in order to unveil the fundamental material formation mechanisms and their optical properties. This approach can provide much faster characterizations that will benefit future in-line process monitoring and enable us to explore the material properties in non-equilibrium states.

I have also worked on various materials, including organic and inorganic, for PV and optoelectronic devices during my Ph.D research. I was able to achieve high performance devices using different semiconductor materials which required a well designed device structure, proper energy band alignment, precise process control and a deep understanding of the material properties. I was the first to demonstrate a high performance fully solution processed solar cell with over 10% efficiency using CuInSe₂ as light absorber. In this work, an unique process design combining metal nanowires and semiconducting nanoparticles was demonstrated to replace traditional ITO as the solution processable transparent electrode. Moreover, the local nanoscale welding effect in solution processed metallic nanowires were investigated, which resulted in the invention of an energy efficient fabrication process that overcomes the challenges for their applications into thermal sensitive devices. In another project, I redesigned the synthesis route of Cu₂ZnSnS₄ nanoparticle precursors as an earth abundant PV absorber and demonstrated a significant improvement (over 40%) of device performance. To overcome the thermodynamic limit of PV efficiency, I also designed and fabricated the tandem PV device structure in collaboration with IBM scientists and successfully achieved over 10 % efficiency for the first time with the combination of organic and amorphous Si solar cells. Last but not least, I investigated the formation process of organic-inorganic hybrid perovskite materials and achieved precise control of the film formation process. Power conversion efficiencies of over 19% was demonstrated within a year effort.

My unique background has prepared me to work in this multidisciplinary research area of material science, chemistry and device physics to develop advanced materials and nanotechnologies and bring in new perspectives and better solutions for energy technologies.

Teaching Interests:

I am interested in teaching most of the major courses for Chemical and Materials Engineering including thermodynamics and kinetics, spectroscopy, microscopy, material design and synthesis, thin film deposition, semiconductor physics, photovoltaic and optoelectronic devices. I have experience as TA and guest lecturers for both graduate and undergraduate level courses including semiconductor devices and fabrication, introduction to solar cells, material physic at UCLA. I am also actively mentoring several UC Berkeley undergraduate students on their research courses in LBNL.

Selected Publications:

1. T.-B. Song, T. Yokoyama,S.Aramaki, M. Kanatzidis “Performance Enhancement of Lead-free Tin-based Perovskite Solar Cells with Reducing Atmosphere-assisted Dispersible Additive” ACS Energy Letter 2, 897-903. (2017)
2. T.-B. Song, T. Yokoyama, C. Stoumpos, J. Logsdon, D. H. Cao, M. R. Wasielewski, S. Aramaki, M. Kanatzidis “Importance of Reducing Vapor Atmosphere in the Fabrication of Sn-based Perovskite Solar Cells” Journal of the American Chemical Society 139 (2), 836-842. (2017)
3. T.-B. Song, Y.S. Rim, F. Liu, B. Bob, S. Ye, Y. Yang “Robust Silver Nanowire Network for Transparent Electrode” ACS Applied Materials & Interface 7 (44), 24601-24607. (2015)
4. T.-B. Song, Q. Chen, H. Zhou, S. Luo, Y. Yang, J. You, Y. Yang “Unraveling Film Transformations and Device Performance of Planar Perovskite Solar Cells” Nano Energy 12, 494-500. (2015)
5. T.-B. Song, Y. Chen, C.-H. Chung, Y. Yang, B. Bob, H.-S. Duan, G. Li, K.-N. Tu, Y.Huang, Y. Yang “Nanoscale Joule Heating and Electromigration Enhanced Ripening of Silver Nanowire Contacts” ACS Nano 8 (3), 2804-2811. (2014)
6. Zhou*, T.-B. Song*, W.-C. Hsu, S. Luo, S. Ye, H.-S. Duan, C.-J. Hsu, W. Yang, Y. Yang “Rational Defect Passivation of Cu₂ZnSn(S,Se)₄ Photovoltaics with Solution-Processed Cu₂ZnSnS₄:Na Nanocrystals” (*These authors contributed equally) Journal of the American Chemical Society 135 (43), 15998-16001. (2013)
7. Zhou, Q. Chen, G. Li, S. Luo, T.-B. Song, H.-S. Duan, Z. Hong, J. You, Y. Liu, Y. Yang “Interface Engineering of Highly Efficient Perovskite Solar Cells” Science 345 (6196), 542-546. (2014)
8. C‐H. Chung, T.‐B. Song, B. Bob, R. Zhu, H.‐S. Duan, Y. Yang “Silver Nanowire Composite Window Layers for Fully Solution‐Deposited Thin‐Film Photovoltaic Devices” Advanced Materials 24 (40), 5499-5504. (2012)