לוח שנה משולב

We can watch crystals grow in the electron microscope by adding atoms one at a time onto a clean surface. The movies tell us about kinetics and thermodynamics but can also be entertaining, frustrating, or both at the same time. I will attempt to share the joy of this type of “in situ” microscopy as we aim to understand how atoms assemble into nanowires or nanocrystals and use the information to control the formation of more complicated nanostructures with new properties

For some time, our group has been focused on the design, synthesis and application of derivatives of boron subphthalocyanines (BsubPcs), a macrocyclic molecule with chelated central boron atom. Our focal point has been and continues to be equally balanced between the basic and applied chemistry of BsubPcs, their application as light absorbing and electronic conducting materials in organic photovoltaics (OPVs)/solar cells.
For this presentation I will outline how we have developed BsubPcs for their application in OPVs and other organic electronic devices. For OPVs, we have developed an approach to their development whereby their basic and applied chemistry is justified by a development cycle which includes their physical chemistry and characterization, their immediate integration into OPVs and based on their indoor stability are placed in the ambient environment to truly address their ultimate application in organic solar cells. Integrated into this cycle is a computational modeling methodology that is used to screen potential BsubPcs for their application in organic electronic devices including OPVs/organic solar cells. Most recently we have identified a pathway to BsubPcs whereby all carbons are bio-sourced and I will highlight how the computational model justified the time and resource commitment to their synthesis and development.
In addition to BsubPcs, we have taken an equal approach to extended -conjugated derivatives of BsubPcs, boron subnaphthalocyanines (BsubNcs); BsubNcs being unique and beneficial materials for OPV application. We have shown that BsubNcs actually become randomly chlorinated during their synthetic preparation and actually then form a mixed alloy composition of chlorinated materials, which we have designated as Cl-ClnBsubNcs. The mixed alloy composition is unique, and has been determined to be a mixture of 24 (more or less) chlorinated BsubNcs despite being a mixture that uniquely forms single crystals. The formation of single crystals is enabled by the chlorine atoms occupying vacancies within the solid state structure, the vacancies being the so-called “bay position” of the BsubNcs structure. During this presentation I will highlight how odd the mixed alloy composition of organic materials is and how hard it has been to separate the mixed alloyed composition. I will also highlight how we are moving forward with purposefully making mixed alloyed compositions of our macrocyclic compounds BsubPcs and BsubNcs fully justified by the potential performance increase in organic solar cells.
Co-authors/investigators will be identified during this presentation.
#--
Some Relevant References.
[1] “Outdoor Performance and Stability of Boron Subphthalocyanines Applied as Electron Acceptors in Fullerene-Free Organic Photovoltaics.” Josey, D.; et al, ACS Energy Lett., 2017, 2(3), 726–732. DOI: 10.1021/acsenergylett.6b00716.
[2] “Boron Subphthalocyanines as Electron Donors in Outdoor Lifetime Monitored Organic Photovoltaic Cells.” Garner, R.K.; et al, Solar Energy Materials and Solar Cells, 2018 176, 331-335. DOI: 10.1016/j.solmat.2017.10.018
[3] “8.4% efficient fullerene-free organic solar cells exploiting long-range exciton energy transfer” Cnops, K.; et al., Nature Comm., 5, Article number: 3406, DOI:10.1038/ncomms4406.
[4] “The mixed and alloyed chemical composition of chloro-(chloro)n-boron subnaphthalocyanines dictates their physical properties and performance in organic photovoltaics.” Dang, J.D.; et al, J. Mat. Chem. A., 2016, 4, 9566-9577. DOI: 10.1039/C6TA02457B
[5] “Phenoxy-(chloro)n-boron subnaphthalocyanines; alloyed mixture, electron-accepting functionality, enhanced solubility for bulk heterojunction organic photovoltaics” Dang, J.D.; et al, ACS Omega, 2018, 3(2), 2093–2103. DOI: 10.1021/acsomega.7b01892.
[6] “The Mixed Alloyed Chemical Composition of Chloro-(chloro)n-Boron Subnaphthalocyanines Dictates Their Performance as Electron-Donating and Hole-Transporting Materials in Organic Photovoltaics” Garner, R.K.; et al, ACS Appl. Energy Materials, 2017, 1(3), 1029-1036. DOI: 10.1021/acsaem.7b00180.
[7] "Outdoor Stability of Chloro-(Chloro)n-Boron Subnaphthalocyanine and Chloro-Boron Subphthalocyanine as Electron Acceptors in Bilayer and Trilayer Organic Photovoltaics" Josey, D.; et al, ACS Applied Energy Materials, 2019, 2(2), 979–986. DOI:10.1021/acsaem.8b01918

Neuronal networks have many tunable parameters such as synaptic strengths that are shaped during learning of a task. The number of degrees of freedom for representing a task can vastly exceed the minimum required for good performance. I will describe recent work that explores the consequences of such additional ‘redundant’ degrees of freedom for learning and for task representation. We find that additional redundancy in network parameters can make a fixed task easier to learn and compensate for deficiencies in learning rules. However, we also find that in a biologically relevant setting where synapses are subject to unavoidable noise there is an upper limit to the level of useful redundancy in a network, suggesting an optimal network size for a given task.