Biwu MaStaff Scientist
Organic and Macromolecular Synthesis Facility
My research focuses on the preparation, characterization and applications of new functional materials, from organic compounds to metallo-organics, polymers, and nanocomposites. These materials show promise for applications in photonics, opto-electronics, nanotechnology and solar energy conversion. Of particular interest are organic solar cells, organic light emitting diodes, transistors, chemical sensors and many other organic or hybrid electronic devices. The major purpose of my research is to study the underlying chemical and physical properties of new materials and understand how molecular structure affects the properties of the materials and their performance in the devices.
Visit The BWM Research Group
- Solution processing of Pigment Based Materials for Organic Solar Cells
Solar cells are among the most promising technologies for the renewable clean energy. Organic solar cells (OSCs) show great ptential due to their low cost of manufacture and fabrication. Driven by new materials, new processing techniques and advanced device concepts, OSC power conversion efficiencies have steadily improved to the 6-8% range. However, many issues remain, including efficiency, lifetime and stability.
To realize OSCs with efficiencies exceeding 10%, our research looks at the great potential in light absorbing organic pigments, which have been widely used in plastic coloration and paints. We focus on the development of new photo-/electro-active soft materials, the real control on morphology leading to ideal donor/acceptor nanophase separation, and the fundamental understanding of device operation. The synthetic approach will involve integrating multiple functional components into a pigment (dye) core to achieve new materials possessing high light absorbing capabilities, high solubility, high charge carrier mobility and nanoscale ordering functionality.
Solution processable subphthalocyanines
Soluble boron subphthalocyanine (SubPc) derivatives have been developed for use as active materials in efficient organic photovoltaic cells. These materials possess unique structural and photophysical properties, i.e. high solubility, low tendency to aggregate, and high extinction coefficients that enable the formation of high performance photovoltaic thin films. Learn more
Bodipy-based polymers, which possess a high absorption coefficient with a bandgap of 1.6 eV, have been used as electron donor in solution-processed bulk heterojunction (BHJ) solar cells containing PCBM as acceptor. A power conversion efficiency (PCE) of 2% has been achieved with Voc of 0.8 eV and Jsc of 4.8 mA cm-2. Learn more
- BongSoo Kim, Biwu Ma, Venkat R. Donuru, Haiying Liu and Jean M. J. Fréchet
- Solution processable subphthalocyanines
- Nanoimprint photovoltaic materials
Nanoimprint lithography represents a highly promising, low cost technique for producing idealized bulk heterojunction OPVs in which electron donors and acceptors interpenetrate to form nanostructured networks. In addition, nanoimprint lithography is compatible with high throughout roll-to-roll processing. Thermal nanoimprinting of a boron subphthalocynamine molecule, 2-allylphenoxy-(subphthalocyaninato)boron(III) (SubPc-A) has been carried out, which represents a class of attractive small-molecular weight organic compounds for organic-based photovoltaics (OPV). The final equilibrium imprinted feature profile strongly depends on the imprinting temperature. The highest feature aspect ratio (or contrast) occurs at a specific window of imprinting temperatures (80−90 °C). X-ray diffraction indicates that the nanoimprint at such a temperature window can induce high-degree molecular stacking, which can help stabilize the imprinted features. Read the research paper [access required].
- New materials and device architectures for white organic light emitting diodes
Bichromophoric Phosphorescent Block Copolymers
Organization of phosphorescent domains in self assembled block copolymers is demonstrated to yield dual emission for white electroluminescence. The block copolymer approach minimizes energy transfer between two colored species by site isolation through morphology control, allowing higher loading concentration of red emitters with improved device performance. Learn more
- Daniel A. Poulsen, Bumjoon J. Kim, Biwu Ma, C. Sebastian Zonte, and Jean M. J. Fréchet
- Bichromophoric Phosphorescent Block Copolymers
Colored phosphorescent polymer nanoparticles
The use of cross-linked polymer nanoparticles was explored to achieve site isolation of different emitters within a single emissive layer in an electroluminescent device. Encapsulation of the iridium emitters within the polymer nanoparticles led to the desired effect with minimal energy transfer from high bandgap chromophores to lower bandgap ones. The nanoparticles were easily dispersed in organic solvent for film casting while preserving particle shape. They behave as light emitting “inks”, enabling the tuning of electroluminescence through simple changes in the ratios of nanoparticles in the emissive film. Read the research paper [access required].
- Haifeng Gao, Daniel A. Poulsen, Biwu Ma, David A. Unruh, Xiaoyong Zhao, Jill E. Millstone and and Jean M. J. Fréchet
- Ma, B., Woo, C. H., Miyamoto, Y., Fréchet, J. M. J., "Solution Processing of a Small Molecule, Subnaphthalocyanine, for Efficient Organic Photovoltaic Cells," Chemistry of Materials, 2009, 21, 1413–1417.
- Kim, B., Ma B., Donuru, V. R.; Liu, H., Fréchet J. M. J., "BODIPY-Backboned Polymers as Electron Donor in Bulk Heterojunction Solar Cells," Chemical Communications, 2010, DOI: 10.1039/b927350f.
- Liang, X.; Chen, T., Jung Y. S., Miyamoto, Y., Han, G.; Cabrini, S., Ma, B., Olynick, D., "Nanoimprint-Induced Molecular-Stacking and Pattern Stabilization in A Solution-Processed Subphthalocyanine Film" ACS Nano, 2010, 4, 2627-2634.
- Gao, H.; Poulsen, D. A., Ma, B., Unruh, D., Zhao, X.; Millstone, J., Fréchet J. M. J., “Site Isolation of Iridium Emitters within Crosslinked Organic Nanoparticles for White Electroluminescence”, Nano Letters, 2010, 10, 1440–1444.
- Poulsen, D. A., Kim, B. J., Ma, B.; Zonte, S., Fréchet, J. M. J., "Site-Isolation in Phosphorescent Bichromophoric Block Copolymers Designed for White Electroluminescence," Advanced Materials, 2010, 22, 77–82.
B.S., 2001, Beijing University of Chemical Technology, Beijing
M.S., 2002, Materials Science, University of Southern California, Los Angeles
Ph.D., 2005, Materials Science, University of Southern California, with Professor Mark E. Thompson: “The photophysics of platinum complexes and their applications in organic light emitting diodes”
Postdoctoral Fellow, 2006-08 UC Berkeley and Lawrence Berkeley Nat Lab, with Professor Jean M. J. Frechet