Electrochemical Advances in Fluorinated/Chlorinated Boron Subphthalocyanines (BsubPcs) and Tetrabenzotriazacorroles (TBCS) Enabled By the Exploration of Their Base Chemistry and Their Application in Organic Voltaics
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 and organic light emitting diodes (OLEDs).

I will begin by presenting our efforts with regards to synthetic variants of BsubPcs and their application in planar heterojunction organic photovoltaic cells (OPVs, organic solar cells, OSCs).[1,2] After summarizing this work, I will then outline our very recent results.

We have made recent observations that during the synthesis of peripherally fluorinated BsubPcs, through the reaction of tetrafluoro phthalonitrile and boron trichloride, that the resulting BsubPc has a significant portion of axial halide exchange yielding a mixture of Cl-F12BsubPc and F-F12BsubPc and separation of the mixture is not possible. The same scenario was observed for the synthesis of Cl-F6BsubPc. Therefore we developed a process to yield high purity F-F12BsubPc and F-F6BsubPc. Thereafter we revisited the electrochemistry of the peripherally fluorinated BsubPcs and their application in OPVs and compared results against peripherally chlorinated BsubPcs. Results will be presented.

During past ECS meetings, we presented the electrochemistry and OPV application of peripherally chlorinated BsubPcs, specifically, BsubPcs with 6 and 12 peripheral chlorine atoms, Cl-Cl6BsubPc and Cl-Cl12BsubPc respectively. Recently we have developed a new chemical process that can yield a unique Cl-Cl9BsubPc and a Cl-Cl6BsubPc alternative. This developed chemistry will be presented and will also include an overview of the electrochemical and OPV performance characteristics that are dependent on the position and frequency of peripheral chlorine atoms.

We have also recently shown that structural analogs to BsubPcs, boron subnaphthalocyanines (BsubNcs) are actually a mixed alloy composition of chlorinated materials designated as Cl-ClnBsubNcs. After establishing the correlation of electrochemical characteristics and OPV performance for Cl-ClnBsubNc we have recently shown that phenoxylated versions of ClnBsubNc are also applicable in BHJ OPVs also as electron accepting materials. More recently we have shown that Cl-ClnBsubNcs when applied as electron donating materials in OPVs have the same performance correlations to the amount of chlorination present and this will be presented.

Finally, we have been exploring the chemistry that yields silicon tetrabenzotriazacorrole derivatives (SiTbcs). We have explored the chemistry using various sized axial ligands. The SiTbcs are formed from bis(hydroxy) silicon phthalocyanine ((OH)2-SiPc) via a simple reductive chemical process using magnesium metal and a chlorosilane in pyridine. The net change is the simple loss of 1 imide nitrogen atom yet the change in properties is significant including electrochemical and photophysical properties and these results will be presented.

Coauthors and coinvestigators will be cited as appropriate throughout the presentation.

References:

[1] Cnops, K.; et al., Nature Comm., 5, Article number: 3406, DOI:10.1038/ncomms4406.

[2] Verreet, B.; et al., Adv. Energy Mater. 2014, 1301413, DOI:10.1002/aenm.201301413.

Our Relevant References:

“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.

“Boron Subphthalocyanines as Electron Donors in Outdoor Lifetime Monitored Organic Photovoltaic Cells.” Garner, R.K.; et al, Solar Energy Materials and Solar Cells, 2017, accepted.

“The mixed and alloyed chemical composition of chloro-(chloro)n-boronsubnaphthalocyanines dictates their physical properties and performance in organic photovoltaics.” Dang, J.D.*; Josey, D.*; Lough, A.; Li, Y.; Sifate, A.*; Lu, Z.H.; Bender, T.P.; J. Mat. Chem. A., 2016, 4, 9566-9577.

“Acceptor Properties of Boron Subphthalocyanines in Fullerene Free Photovoltaics.” Beaumont, N.; Castrucci, J.S.; Sullivan, P.; Morse, G.E.; Paton, A.S.; Lu, Z.H.; Bender, T.P.*; Jones, T.S.; J. Phys. Chem. C, 2014, 118(27) 14813–14823.

“The Position and Frequency of Fluorine Atoms Changes the Electron Donor/Acceptor Properties of Fluorophenoxy Silicon Phthalocyanines within Organic Photovoltaic Devices” Lessard, B.H.; Grant. T.; White, R.; Thibau, E.; Lu, Z-H.; Bender, T.P.*; J. Mater. Chem. C., 2015, 24512-24524.