Electrochemical Advances in Boron Subnaphthalocyanines (BsubNcs) for Organic Photovoltaic Applications: The Ambient Stability of Bsubnc Mixed Alloys; Their Separation and Electrochemical Properties; And Chemical Progresses Towards Pure Bsubncs to Yield Their Individual Electrochemical Evaluation
Authors: Bender Timothy P 
Published: February 2020

For some time, our group has been focused on the design, synthesis and application of derivatives of boron subphthalocyanines (BsubPcs). Our focal point has been and continues to be equally between the basic chemistry of BsubPcs and their application in organic electronic devices with a focus on two specific device applications, organic photovoltaics (OPVs)/solar cells[1,2] and organic light emitting diodes (OLEDs). More recently, we have taken an equal approach to derivatives similar to BsubPcs, boron subnaphthalocyanines (BsubNcs); BsubNcs being unique and beneficial materials for OPV application.[3]

We have recently 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.[4] The mixed alloy composition is unique, and has been determined to be a mixture of 24 (more or less) chlorinated BsubNcs that despite being a mixture form 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. After establishing the correlation of electrochemical characteristics and OPV performance for Cl-ClnBsubNcs, we have recently shown that phenoxylated versions of ClnBsubNc are also a mixed alloy and applicable in BHJ OPVs also as electron accepting materials.[5] We have also shown that Cl-ClnBsubNcs when applied as electron donating materials in OPVs have the same performance correlations to the amount of chlorination present.[6] We have also shown that BsubNcs are equally stable within an OPV in the ambient environment compared with BsubPcs.[7] This accumulation of properties led us to consider how to separate the alloyed mixtures and how to prepare pure BsubNcs.

During this presentation I will describe a chemical pathway to enable the separation of the mixed alloys of BsubNcs. We found that not all 24 (more or less) isomers can be separated, yet this process has enabled a more detailed electrochemical characterization and correlation to amount of halogenation. I will also describe a chemical pathway to pure BsubNcs, avoiding halogenation/chlorination in the bay position. This pathway enables a detailed characterization of a pure BsubNc including its electrochemical properties. Finally, if completed by the presentation time, I will also describe a chemical pathway to enable complete halogenation of the bay-position of a BsubNc. This pathway then enabled the characterization and therefore the impact on the electrochemical and other physical properties of complete bay-position halogenation.

Co-authors/investigators will be identified during this presentation.

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.

[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, 2018, submitted.

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