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Abstract: In this seminar, we will focus on our recent work on two different thin film systems – metal halide perovskites and organic semiconductors.For one, through proper control of processing, we are able to realize pinhole free organic semiconductor films with single crystal grains with mm dimensions. We have found that transport in these films is considerably improved compared to disordered films, and that organic solar cells incorporating these long-range-ordered films exhibit highly delocalized, and band-like charge transfer (CT) states, contributing to noticeably lower energy losses. We will discuss these aspects and our understanding to-date of which molecules are amenable to the formation of such films, and how to propagate their growth. Also, organic hole transport materials (HTMs) are ubiquitous in halide perovskite solar cells, but what is less well known is that shallow HTMs that facilitate hole extraction from the perovskite also enable halogen transport. We will present our understanding of this phenomenon, as well as impacts to devices with regard to Au diffusion.

Bio: Barry Rand earned a BE in electrical engineering from The Cooper Union in 2001. Then he received MA and PhD degrees in electrical engineering from Princeton University, in 2003 and 2007, respectively. From 2007 to 2013, he was at imec in Leuven, Belgium, ultimately as a principal scientist, researching the understanding, optimization, and manufacturability of thin-film solar cells. Since 2013, he is in the Department of Electrical Engineering and Andlinger Center for Energy and the Environment at Princeton University, currently as a Professor. Prof. Rand’s research interests highlight the border between electrical engineering, materials science, chemistry, and applied physics, covering electronic and optoelectronic thin-films and devices. He has authored over 160 refereed journal publications, has 25 issued US patents, and has received the 3M Nontenured Faculty Award (2014), DuPont Young Professor Award (2015), DARPA Young Faculty Award (2015), and ONR Young Investigator Program Award (2016).

Dr. Shanina Sanders Johnson

Ph.D., University of North Carolina at Chapel Hill

B.S., Hampton University

At Spelman since 2011, promoted to Associate Professor recently

Abstract: Dr. Johnson's work has involved implementing culturally relevant pedagogies into organic chemistry lecture and laboratories. Activities that provide context to chemistry have been created and implemented to allow for incorporation of student background, interests, and experiences into the curriculum. These strategies allow students to see the relevance of science, reflect on their science identity, and connect their personal experiences and knowledge to their learning. Additionally, allowing for cultural context in the curriculum supports diversity within the classroom on multiple levels. This type of strategy is ultimately aimed at not only diversifying chemistry but also ushering in social change that provides for a more equitable field.  

Abstract: Halide perovskites are exciting new semiconductors that show great promising in low cost and high-performance optoelectronics devices including solar cells, LEDs, photodetectors, lasers, etc. However, the poor stability is limiting their practical use. In this talk, I will present the development of a new family of stable organic-inorganic hybrid electronic materials, namely, Organic Semiconductor-Incorporated Perovskites (OSiP). Energy transfer and charge transfer between adjacent organic and inorganic layers are extremely fast and efficient, owing to the atomically-flat interface and ultra-small interlayer distance. Moreover, the rigid conjugated ligands dramatically enhance materials’ chemical stability and suppresses solid-state ion diffusion and electron-photon coupling, making them promising for many applications. Based on this, we demonstrate for the first time an epitaxial halide perovskite heterostructure with near atomically-sharp interface, which pave the way for perovskite nanoelectronics and nanophotonics. Finally, using this stable and solution-processable OSiPs, we demonstrate the fabrication of high-quality thin films, which enable highly stable and efficient solar cells and LEDs.

Bio: Dr. Letian Dou is currently the Charles Davidson Associate Professor of Chemical Engineering at Purdue University. He obtained his B.S. in ÌÇÐÄvlog¹Ù·½Èë¿Ú from Peking University in 2009 and Ph.D in Materials Science and Engineering from UCLA in 2014. From 2014 to 2017, he was a postdoctoral fellow at the Department of ÌÇÐÄvlog¹Ù·½Èë¿Ú, University of California-Berkeley and Materials Science Division, Lawrence Berkeley National Laboratory. His research interest includes the design and synthesis of organic-inorganic hybrid materials and low-dimensional materials, fundamental understanding of the structure-property relationships, as well as applications in high performance electronic and optoelectronic devices. He is a recipient of AIChE Owens Corning Early Career Award (2022), NSF CAREER Award (2021), Advanced Materials Rising Stars Award (2021), Office of Naval Research Young Investigator Award (2019), Highly Cited Researcher in Cross-Fields (2019-2022), MIT Technology Review Innovators Under 35-China Award (2018), and MRS Graduate Student Award (2014).

Abstract: Supramolecular gelation is a fascinating self-assembly process that closely mimics important natural and biological events. The supramolecular nature of such materials imparts the system with reversibility and adaptivity. The individual or collective contributions of various non-covalent interactions, such as hydrogen bonding, π– Ï€ stacking, metal–ligand coordination, host–guest interactions, and van der Waals interactions, are at the focal point of the structural evolution during an assembly process. Supramolecular gels have been studied extensively in the last few decades, mostly by exploiting the functional outputs for technological and medicinal applications. In comparison, pure structural investigations of supramolecular gel materials are rather limited. The lack of convincing structural data has multiple implications. The two most crucial factors for structural investigations are the experimental time scale and the sensitivity of the measurements towards structural evolution. Herein, we will investigate self-assembly processes of supramolecular nanoassmeblies under ambient versus non-ambient conditions. Specifically, we will probe how real-time measurements give valuable insights about nucleation and self-assembly of materials. The information obtained yields valuable information about structure-function correlation of materials which could have applications in several areas, including pharmaceutics and personal care. 

Bio: Dr. Harshita Kumari, is an Associate Professor in the Division of Pharmaceutical Sciences at University of Cincinnati. Dr. Kumari’s work in the area of solution chemistry of supramolecular complexes is widely recognized. She integrates neutron scattering with supramolecular chemistry to unravel structural altercations in solution.

Her current research focuses on integrating principles of modern biophysics into material and formulation science towards the development of novel skin care, oral care and hair care products. Her research projects focus on understanding mechanisms of delivery and deposition of actives onto the skin/hair and elucidating the parameters to control them. In addition, her research focuses on developing methods to construct novel nanometric delivery vehicles, based on the principles of self-assembly and molecular recognition. Her work is published in several peer reviewed journals.