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Title: Devices emerging from controlling organic and metal halide perovskite energetics and morphology
Abstract: In this seminar, we will focus on our recent work on two different thin film systems – metal halide perovskites and organic semiconductors.
For organic semiconductors, through proper control of processing, we are able to realize pinhole free films with grains of up to 500 μm in extent. we have found that charge transfer (CT) states incorporating these long-range-ordered films can be highly delocalized, contributing to noticeably lower energy losses. Also, we have discovered that relative energies of CT states with respect to singlet and triplet energy levels are critical when considering devices that exploit multiple exciton processes such as singlet fission and its complement, triplet-triplet annihilation (or triplet fusion). We will discuss these aspects and their implications for more efficient organic solar cell function.
Hybrid inorganic-organic perovskite materials, most commonly methylammonium lead triiodide (MAPbI3), have captured significant interest in the thin film optoelectronics community due to their impressive optical and electrical properties. For light emitting diodes (LEDs), we have established a general protocol for preparing ultrathin, smooth, passivated, and pinhole free films of metal halide perovskites with various compositions, by incorporating bulky organoammonium halide additives to the stoichiometric 3D perovskite precursors. Here, we will present this approach as well as our understanding for how to select bulky organoammonium additives. LEDs produced in this way are capable of exceeding 17% external quantum efficiency, exhibit significantly improved stability, and are capable of being as flexible as organic electronic thin films. Finally, they allow for stabilizing mixed halide (I and Br) and mixed Pb-Sn stoichiometries such that we can tune emission from the green to near infrared. Also, we will show how these smooth films can be employed in optically pumped laser structures that tunable and capable of sustaining cw emission.
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 an Associate 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 approximately 125 refereed journal publications, has 20 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).