Interview: Feilong Liu


On April 11, MSI held its 4th Annual Research Exhibition. This event included a judged poster competition for our users. The winner of this year’s competition was Feilong Liu, who submitted a poster entitled, “Numerical Modeling of Organic Semiconductor Heterostructure Devices.” Mr. Liu is a graduate student in the research group of Professor P. Paul Ruden in the Department of Electrical and Computer Engineering. MSI recently met with with Mr. Liu to discuss his research.


MSI: How long have you used MSI resources?


Feilong Liu: I started using MSI in 2010, so about three years. I came to the University during the fall semester of 2009.


MSI: What type of research do you use MSI for?


FL: Basically we use MSI for the numerical calculations of our organic hetero-structured device model. Organic-based semiconductors have an advantage in that their flexibility, low cost, and ease of fabrication makes these devices potentially very attractive for many different applications. The big difference between what our research group does and what other groups do is that, whereas they focus on the fabrication of the devices we focus on the theoretical perspectives. We try to understand the device physics. So, this is where MSI really helps out, we use MSI resources to do the physics-based calculations of the device model.  


MSI: Could you talk about what your poster describes?


FL: The poster shows a complete device model. It shows the calculation for the electrostatics of the device. We do this by splitting the device into hundreds of segments and each of these segments has multiple differential equations attached to it. This leaves us with thousands of coupled equations that we need to use MSI resources to solve. With the results we can explore two types of real applications. The first is the light-emitting diode that converts electricity to light. The second is the photovoltaic cells, which conversely converts light to electricity. The poster shows that our model can work well for both applications.


MSI: In regards to the calculations you do, are there any systems here at MSI that you use in particular?


FL: I remotely access the Laboratory Interactive pool of resources to run a Fortran compiler. 


MSI: Would you say your research is geared towards immediate applications or is more theoretical?


FL: First, we wanted to understand what is going on with the devices. Next, we asked, what can we do to improve existing devices? The recent research of our group has been aimed at improving the performance of the device models. What we do is come up with ideas of how to improve the performance and efficiency of devices like LEDs and solar panels, and these ideas enter the development of these products.


MSI: Would you like to continue this research once you become a PI of your own research group?


FL: I think this is a great project and group to be a part of. This project had been ongoing when I became a part of it. What I did was to improve the previously established model, which was basically generic for any bilayer structure. I incorporated the characteristic microscopic processes for organic-based devices. I think that in the future what needs to be done is to extend our model to more complicated devices. For instance the model we have now is applicable to a bilayer structure, with one layer of Material A and the other of Material B. In real experiments, however, it is becoming very popular to use an interpenetrated structure; people call this a bulk heterojunction. Going forward I think it would be very interesting to figure out how to model this type of structure.


MSI: Do you think MSI resources will be an important part of your future research?


FL: Of course, if I have access to MSI resources in the future it will be of great importance to my research. It is a very nice thing to have and something I hope to enjoy for some time to come. 


NOTE: Mr. Liu was the lead author on a paper published in the journal Applied Physics Letters about this topic: "Electrostatic Capacitance in Single and Double Layer Organic Diodes," FL Liu, PP Ruden, IH Campbell, DL Smith, Applied Physics Letters, 101(2):023501, DOI: 10.1063/1.4734379 (2012).