Boron Subphthalocyanines, Boron Subnaphthalocyanines and Silicon Phthalocyanines As Non-Fullerene Electron Accepting Materials in Organic Photovoltaics (and Tetrabenzocorroles as Complimentary Electron Donating Materials)
Authors: Bender Timothy P 
Published: February 2020

For some time, our group has been focused on the design and synthesis of derivatives of boron subphthalocyanine (BsubPc) for application in organic electronics with a specific focus on organic photovoltaics and light emitting diodes; during this presentation however I will focus specifically on their application in organic photovoltaics.

I will begin by focusing on 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 where we took BsubPc based planar heterojunction organic photovoltaic cells and put them on the roof of our building in downtown Toronto during the summers of 2015 and 2016 in the ambient environment. What we found was that when BsubPcs are applied as electron accepting materials they are remarkably stable and maintain a 4% PCE over time. On the flipside, when applied as electron donating materials the stability of the paired material, C60, fullerene, dictates the overall stability of the devices. Additionally we have used a novel method to map out the degradation pathway of the OPVs which will be described. We were able to ultimately form a structure property relationship to their stability in the ambient environment.

In parallel we have also been exploring the concept of complementary absorption engineering by either the chemical modification of BsubPcs or by pairing BsubPcs with alternative materials having complementary absorption profiles. For example, we have recently shown that after firming up the chemical structure of phosphorus oxy tetrabenzotriazacorrole [POTbc, a phthalocyanine analogue] that the pairing of a BsubPc with yields a unique gray organic photovoltaic cell absorbing broadly across the visible spectrum.

Our group’s has recently began the exploration of the bulk-heterojunction OPV space whereby BsubPcs are again electron accepting fullerene alternatives, although we are not the first to do so.[3,4] I will articulate our recent findings. 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 how phenoxylated versions of ClnBsubNc are also applicable in BHJ OPVs also as electron accepting materials. We have also explored the potential of chemistry variations to yield pure examples of BsubNcs. Time permitting this will be outlined along with electrochemical characterization.

Finally, during last year’s meeting, I outlined how our group’s recent exploration of other p-block metal phthalocyanines (Pcs) yielded the conclusion that silicon phthalocyanines (SiPcs) can also be applied as fullerene alternatives/acceptors in organic photovoltaic cells. Our conclusion at the time was that phenoxylation enhances the performance of SiPcs as an electron transporting/accepting materials. Over the past year we have enhanced this conclusion and formed an initial structure property relationship that gives a road map to synthetic alternatives of SiPcs that may ultimately yield higher performing OPVs. The potential applications have also been expanded beyond SiPcs in PHJ OPVs whereby we have shown that they can be equally applied as electron accepting fullerene alternatives in the BHJ OPV space as well. I will outline this structure property relationship and our future work in this area.

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.

[2] Ebenhoch, B.; et al., J. Mater. Chem. A, 2015, 3, 7345.

[3] Duan, C.; et al., Angew. Chem. Int. Ed., 2016, DOI: 10.1002/anie.201608644.

Our Relevant References:

“Outdoor Performance and Stability of Boron Subphthalocyanines Applied as Electron Acceptors in Fullerene-Free Organic Photovoltaics.” Josey, D.; et al, submitted.

“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.