aspuru-list March 2016

aspuru-list@lists.fas.harvard.edu

23 participants
63 discussions

[Aspuru-Guzik Group List] Excitonics/Perovskites Seminar: Eric Hoke, TOMORROW: Wed. Mar 9 at 4:30 pm

by Catherine M Bourgeois

Please post and forward to your groups. CENTER FOR EXCITONICS Seminar Series: Perovskite Seminar: Reversible and irreversible ion migration processes in lead halide perovskites for photovoltaics March 9, 2016 at 4:30 PM/36-462 Eric Hoke Standord University, Draper Laboratory [hoke-eric] Lead hybrid perovskites are a promising family of photovoltaic absorber materials that have achieved power conversion efficiencies of over 20%. Lead halide perovskites are ionic materials with a low lattice energy which are unusual properties for a photovoltaic material. It has been conjectured that this ionic character may be responsible for the material's defect-tolerant optoelectronic properties that have enabled its success as an efficient photovoltaic material. However, lead halide perovskites are highly susceptible to ion migratory processes which pose a significant challenge to the commercialization of stable devices. In this talk, I will present experimental evidence for a variety of ionic migration processes in perovskite thin films resulting from optical or electrical excitation. We observe from in-situ XRD measurements that bromine-rich (0.2<x<1) CH3NH3Pb(BrxI1-x)3 and other mixed-halide perovskites undergo a structural transformation under photoexcitation, segregating into two distinct perovskite phases over the course of minutes. The optical properties are also changed by this transformation resulting in the appearance of intense photoluminescence and absorption features from a lower bandgap phase. The perovskite surprisingly reverts back to its original structure and starting optical spectra when left in the dark. We suggest that photoexcitation induces halide segregation, resulting in iodide-rich domains. These lower bandgap domains act as traps and are likely responsible for the poor open circuit voltages generated by large bandgap, bromine-rich (0.2<x<1) CH3NH3Pb(BrxI1-x)3 solar cells. Perovskite solar cells frequently exhibit hysteretic behavior, which is greatly aggravated by the presence of moisture. The influence of electric field and moisture on perovskite films was investigated using a combination of photocurrent, optical, Raman, and Auger mapping techniques on lateral thin-film devices. These studies suggest that irreversible field-induced degradation in air occurs via a hydrated phase, in which the organic cation is loosely bound and can drift in response to an electric field, finally degrading the material to PbI2. Eric Hoke was recently the Associate Director of the Center of Advanced Molecular Photovoltaics at Stanford University. He completed his PhD from Stanford University in 2012 as a Fannie & John Hertz fellow and National Science Foundation Graduate Research fellow where he studied light harvesting mechanisms and degradation processes in organic photovoltaics and dye sensitized solar cells. Dr. Hoke recently joined Draper Laboratory as a member of Senior Technical Staff where he is developing imaging systems. This talk is part of the Perovskites Seminar Series organized by Sam Stranks and sponsored by the Center for Excitonics. For more info contact Sam: stranks(a)mit.edu<mailto:stranks@mit.edu> Light refreshments will be served The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S. Department Of Energy, Office Of Science And Office Of Basic Energy Sciences

8 years, 1 month

[Aspuru-Guzik Group List] Explain this to us, dear Jacob!

by Adrian Jinich

This looks like a fascinating paper that Jacob could explain to us in a journal club session :) http://www.nature.com/nature/journal/v531/n7592/full/nature16989.html

8 years, 1 month

[Aspuru-Guzik Group List] Euro Request

by Marlon Cummings

Group: I'm looking to purchase ~150 euros. If you have some, I'll be happy to take them off your hands. Please, this is a personal request, DO NOT respond to All! Thanks, MC -------------- *Marlon G. CummingsLab Manager, Aspuru-Guzik GroupMallinckrodt M136Department of Chemistry and Chemical BiologyHarvard University12 Oxford StreetCambridge, MA 02138617-496-9964617-496-9411 (fax)http://aspuru.chem.harvard.edu/ <http://aspuru.chem.harvard.edu/>*

8 years, 1 month

[Aspuru-Guzik Group List] aspuru-guzik-dev queue now available

by Sam Blau

Hey everyone, As per the request last week at group meeting, RC has created a debug / development queue for our group which can be accessed with -p aspuru-guzik-dev. Jobs in this queue can have at max a 30 minute walltime. Note that right now the queue contains one node, aka 32 cores. Please feel free to start using this queue, and let me know if you encounter any issues. Sam

8 years, 2 months

[Aspuru-Guzik Group List] March 9, 2016 - ITAMP/HQOC Joint Quantum Sciences Seminar: Herwig Ott

by Ploucha, Clare Dolores

HQOC/ITAMP Joint Quantum Sciences Seminar Wednesday, March 9, 2016 4:00 PM, Jefferson 250 Prof. Herwig Ott "Butterfly Molecules in a Bose-Einstein Condensate" This talk will give an overview of recent experiments in my group studying Rydberg excitations and their dynamics in ultra cold quantum gases. We use ionization processes of Rydberg atoms and molecules as a continuous probe of the system. For very small atomic samples with dimensions of a few micrometers, we reach the superatom limit, where only one excitation fits into the sample at the same time. For increasing size, driving strength and for finite detuning we observe the transition to a multiple excitation regime, where small clusters and correlated dynamics appear. For large Bose-Einstein condensates these clusters contain several hundred excitations and lead strongly correlated ion bursts emitted from the system. The discovery of Rydberg molecules offers another route to study degenerate quantum gases. Taking advantage of a single-photon excitation scheme to molecular Rydberg states, we can continuously measure the number of produced molecules. This has allowed us to probe in real time the double occupancy during a sweep over the superfluid to Mott insulator transition. Butterfly molecules are a special type of Rydberg molecules with exceptional properties. Using a single photon excitation to a Rydberg p-state, we observe for the first time these molecules. Due to their large dipole moment in combination with a small bond length, we resolve the rotational and pendular structure in an electric field. This opens new possibilities to study Rydberg molecules with long-range interactions in optical lattices. Dr. Richard Schmidt "A mesoscopic Rydberg impurity in an atomic quantum gas" Impurity problems have been at the forefront of research in condensed matter physics for several decades. In this talk, we show that Rydberg impurity excitations in ultracold quantum gases present a new frontier in impurity research. Here vastly different energy scales compete, signified in deeply bound Rydberg molecules of mesoscopic size. This situation poses a new challenge for theoretical physics and necessitates the confluence of methods ranging from mesoscopic to atomic physics. In our work, we develop a novel many-body theory for the non-equilibrium dynamics of giant impurity excitations Bose gases. Such single Rydberg impurity excitations have recently been observed, and we demonstrate that these observations can be understood from our theoretical approach which incorporates atomic and many-body theory. The crossover from few-body dynamics to quantum many-body collective behavior - manifest in the appearance of a novel superpolaronic state - is elucidated in an unified functional determinant approach, valid at zero and finite temperature. The time-dependent formalism is not restricted to Rydberg systems but can be generally applied to impurities in bosonic and fermionic environments and opens new possibilities to study impurity dynamics in mesoscopic systems. Reference [1] R. Schmidt, H. R. Sadeghpour, and E. Demler, arXiv:1510.09183 (2015). Student Presentation from 4:00-4:10 PM Refreshments Served from 4:00-4:30 PM Guest Presentation from 4:30-6:00 PM -- Clare Ploucha Faculty Assistant to Professors Lukin & Greiner and their labs Department of Physics 17 Oxford St., Lyman 324A Cambridge, MA 02138 P. (617) 496-2544

8 years, 2 months

[Aspuru-Guzik Group List] Excitonics/Perovskites Seminar: Eric Hoke, Wed. Mar 9 at 4:30 pm

by Catherine M Bourgeois

CENTER FOR EXCITONICS Seminar Series: Reversible and irreversible ion migration processes in lead halide perovskites for photovoltaics March 9, 2016 at 4:30 PM/36-462 Eric Hoke Standord University, Draper Laboratory [hoke-eric] Lead hybrid perovskites are a promising family of photovoltaic absorber materials that have achieved power conversion efficiencies of over 20%. Lead halide perovskites are ionic materials with a low lattice energy which are unusual properties for a photovoltaic material. It has been conjectured that this ionic character may be responsible for the material's defect-tolerant optoelectronic properties that have enabled its success as an efficient photovoltaic material. However, lead halide perovskites are highly susceptible to ion migratory processes which pose a significant challenge to the commercialization of stable devices. In this talk, I will present experimental evidence for a variety of ionic migration processes in perovskite thin films resulting from optical or electrical excitation. We observe from in-situ XRD measurements that bromine-rich (0.2<x<1) CH3NH3Pb(BrxI1-x)3 and other mixed-halide perovskites undergo a structural transformation under photoexcitation, segregating into two distinct perovskite phases over the course of minutes. The optical properties are also changed by this transformation resulting in the appearance of intense photoluminescence and absorption features from a lower bandgap phase. The perovskite surprisingly reverts back to its original structure and starting optical spectra when left in the dark. We suggest that photoexcitation induces halide segregation, resulting in iodide-rich domains. These lower bandgap domains act as traps and are likely responsible for the poor open circuit voltages generated by large bandgap, bromine-rich (0.2<x<1) CH3NH3Pb(BrxI1-x)3 solar cells. Perovskite solar cells frequently exhibit hysteretic behavior, which is greatly aggravated by the presence of moisture. The influence of electric field and moisture on perovskite films was investigated using a combination of photocurrent, optical, Raman, and Auger mapping techniques on lateral thin-film devices. These studies suggest that irreversible field-induced degradation in air occurs via a hydrated phase, in which the organic cation is loosely bound and can drift in response to an electric field, finally degrading the material to PbI2. Eric Hoke was recently the Associate Director of the Center of Advanced Molecular Photovoltaics at Stanford University. He completed his PhD from Stanford University in 2012 as a Fannie & John Hertz fellow and National Science Foundation Graduate Research fellow where he studied light harvesting mechanisms and degradation processes in organic photovoltaics and dye sensitized solar cells. Dr. Hoke recently joined Draper Laboratory as a member of Senior Technical Staff where he is developing imaging systems. This talk is part of the Perovskites Seminar Series organized by Sam Stranks and sponsored by the Center for Excitonics. For more info contact Sam: stranks(a)mit.edu<mailto:stranks@mit.edu> Light refreshments will be served The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S. Department Of Energy, Office Of Science And Office Of Basic Energy Sciences

8 years, 2 months

[Aspuru-Guzik Group List] Dwayne Miller Seminar Today

by Doran Bennett

Hi Everyone, Dwayne Miller (Toronto) is giving the first of two seminars today at MIT. It is worth noting that Dwayne runs a very strong spectroscopy group and is the co-director for CIFAR's Molecular Architecture of Life <http://www.cifar.ca/molecular-architecture-of-life/> program. The talk today is titled: *Mapping Atomic Motions with Ultrabright Electrons: The Chemists' Gedanken Experiment Enters the Lab Frame.* *It starts at 4:30 pm today*, so interested parties will need to leave very shortly after group meeting ends. The talk tomorrow is titled: *Do We Live in a Quantum World? A New Twist. * All the best, Doran

8 years, 2 months

[Aspuru-Guzik Group List] [qip] Friday the 4th

by Edward Farhi

Hi Quanta We will meet tomorrow (Friday) at 11:00. Aram is going to tell you about his recent work with me. See you there. Eddie --------------------------------------------------------- Edward Farhi Cecil and Ida Green Professor of Physics Director Center for Theoretical Physics Massachusetts Institute of Technology 6-300 Cambridge Massachusetts 02139 617-253-4871 --------------------------------------------------------- _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

8 years, 2 months

[Aspuru-Guzik Group List] Group Meeting, Mar 03, 2:30 PM, Div Room

by Ian Kivlichan

Hi all, Prof. Afshan Mohajeri has been visiting the group from Shiraz University during her sabbatical. Tomorrow she will give group meeting in the Div Room at 2:30. See below for the title and abstract. Best, Ian ------------------------------------- Speaker: Afshan Mohajeri Title: 1- Fullerene-based materials for solar cell applications 2- Utilizing Bayesian approach for the accurate description of non-covalent interactions Abstract: First I present one of my recent publications about the application of fullerene derivatives as the key materials for high performance polymer solar cells. We have performed density functional theory calculations to investigate the electronic structures and magnetic properties of several representative C60 fullerene derivatives, seeking ways to improve their efficiency as acceptor of photovoltaic devices. Various quantum chemical properties have been employed to establish several correlation relationships for prediction of *V*OC of fullerene based solar cells. The obtained structure-property correlations opens the ways for manipulating fullerene derivatives and finding the best fullerene acceptor match for P3HT donor. Next I briefly explain my research at Harvard University which is about utilizing Bayesian approach for the description of non-covalent interactions.

8 years, 2 months

[Aspuru-Guzik Group List] Group lunch Wednesday, 3/16, 12pm

by Jennifer Wei

Hi everyone, Thanks for the responses! Based on the survey results, the first group lunch will be Wednesday 3/16, at 12pm, and we will be going to an Indian buffet. I'll email that week to settle the details. We can also discuss how we want to schedule future lunches. Cheers, Jennifer

8 years, 2 months

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aspuru-list March 2016