Princeton Institute for the Science and Technology of Materials (PRISM)

From left, Prof. Jim Sturm, PRISM Director, GPEC Co-winners Sushobhan Avasthi and Bahman Hekmatshoar, and PRISM Associate Academic Director Prof. Craig Arnold. (Photo by Sheila Gunning)

Sushobhan Avasthi, a graduate student in Electrical Engineering, came to Princeton from the Indian Institute of Technology in Kanpur.   He is a member of the group of James C. Sturm, William and Edna Macaleer Professor of Engineering and Applied Science, and Director of the Princeton Institute for the Science and Technology of Materials (PRISM).  Sushobhan has done pioneering work on the fundamental properties of the interfaces between organic/inorganic semiconductors, and their application to photovoltaics.  Prof. Sturm writes “Sushobhan showed for the first time how monolayers of certain semiconducting organic molecules could “passivate” the otherwise detrimental effects of dangling bonds at the silicon surface.  This advance enables one to finally be able to engineer the silicon/organic hybrid structures for photovoltaics, and thus take advantage of the best properties of both organic and inorganic materials.”  In interdisciplinary fashion, he has interacted extensively with the groups of Jeff Schwartz in Chemistry, Antoine Kahn in Electrical Engineering, and Lynn Loo in Chemical Engineering to combine surface chemistry and surface science with semiconductor engineering.  Last year he presented one application of his work to increase solar cell efficiency at the IEEE Photovoltaic Specialists Conference, and at the December 2009 Symposium of the Materials Research Society.  Sushobhan's work, "Stability of Electrical Properties of Silicon (100) Surfaces Passivated with 9, 10-Phenanthrenequinone,” was recognized with a Best Student Poster Award.  

 Bahman Hekmatshoar was a graduate student in Electrical Engineering at Princeton, co-advised by Professors James C. Sturm and Sigurd Wagner.  He received his BS and MS degrees from the University of Tehran, Iran, before coming to Princeton.  His work at Princeton centered on amorphous silicon, a semiconductor which can be deposited over large areas on glass or plastic at low cost, and hence is widely used for solar and display applications.  Bahman focused on overcoming the fundamental long-term degradation mechanisms in amorphous silicon thin film transistors (a-Si TFT’s), and integrating a-Si TFT’s to drive organic light-emitting diodes for future generations of flexible displays.  Prof. Sturm notes that “due to its amorphous nature and resulting strained bonds, amorphous silicon is inherently unstable, causing great uncertainty to our ability to improve performance in future applications.  By directly addressing the root causes of the instability by material engineering in a novel and unexpected way, Bahman was able to improve the stability of a-Si TFT’s by a factor of over 1000 compared to what was previously thought possible.”  He was honored with an Outstanding Graduate Student Award by the Materials Research Society, and is currently working at IBM Watson Research Center on applications of amorphous silicon to photovoltaics. 

David G. Kwabi attends the School of Engineering and Applied Science (SEAS) Award ceremony on Class Day, May 31, 2010.  (Photo by Frank Wojciechowski)

Undergraduate GPEC winner David G. Kwabi of the Mechanical and Aerospace Engineeing (MAE) Department completed an excellent senior thesis on the failure of mechanisms in flexible and organic electronic structures entitled "Adhesion and Failure in Stretchable Organic Electronic Structures" states Prof. Wole Soboyejo, David's advisor. 

David was also co-winner of the Morgan W. McKinzie '93 Senior Thesis Prize for the best thesis in MAE.  He graduates with honors, was inducted into the Sigma Xi Scientific Research Society and completed a certificate program in Materials Science and Engineering. David came to Princeton from Sos-Hermann Gmeiner International College (high-school) in Ghana. He heads to MIT for graduate school in the fall. Congratulations, David!

Abstract:  This work presents the results of an experimental study on adhesion and stretching of organic electronic structures that are relevant to organic solar cells.  The adhesion between bi-material pairs that are relevant to these systems is measured using atomic force microscopy techniques.  The effects of stretching are then examined by deforming poly-dimethly-siloxane (PDMS) substrates with model organic solar cells deposited on plasma-treated surfaces.  Residual stress is characterized using wrinkling patterns observed.  Degradation  mechanisms of Au films on PDMS at different thicknesses are examined to shed light on similar behavior in the stretched devices.  The implications of these results are then examined for the future development of stretchable and flexible organic solar cells and organic light-emitting devices.