Impact of Molecular Orientation and Spontaneous Interfacial Mixing on the Performance of Organic Solar Cells

Handle URI:
http://hdl.handle.net/10754/561612
Title:
Impact of Molecular Orientation and Spontaneous Interfacial Mixing on the Performance of Organic Solar Cells
Authors:
Ngongang Ndjawa, Guy Olivier ( 0000-0001-7400-9540 ) ; Graham, Kenneth; Li, Ruipeng; Conron, Sarah M; Erwin, Patrick; Chou, Kang Wei; Burkhard, George; Zhao, Kui ( 0000-0001-9348-7943 ) ; Hoke, Eric T.; Thompson, Mark E; McGehee, Michael D.; Amassian, Aram ( 0000-0002-5734-1194 )
Abstract:
A critically important question that must be answered to understand how organic solar cells operate and should be improved is how the orientation of the donor and acceptor molecules at the interface influences exciton diffusion, exciton dissociation by electron transfer and recombination. It is exceedingly difficult to probe the orientation in bulk heterojunctions because there are many interfaces and they are arranged with varying angles with respect to the substrate. One of the best ways to study the interface is to make bilayer solar cells with just one donor-acceptor interface. Zinc phthalocyanine is particularly interesting to study because its orientation can be adjusted by using a 2-nm-thick copper iodide seed layer before it is deposited. Previous studies have claimed that solar cells in which fullerene acceptor molecules touch the face of zinc phthalocyanine have more current than ones in which the fullerenes touch the edge of zinc phthalocyanine because of suppressed recombination. We have more thoroughly characterized the system using in situ x-ray photoelectron spectroscopy and found that the interfaces are not as sharp as previous studies claimed when formed at room temperature or above. Fullerenes have a much stronger tendency to mix into the face-on films than into the edge-on films. Moreover we show that almost all of the increase in the current with face-on films can be attributed to improved exciton diffusion and to the formation of a spontaneously mixed interface, not suppressed recombination. This work highlights the importance of spontaneous interfacial molecular mixing in organic solar cells, the extent of which depends on molecular orientation of frontier molecules in donor domains.
KAUST Department:
Physical Sciences and Engineering (PSE) Division; Solar and Photovoltaic Engineering Research Center (SPERC)
Citation:
Impact of Molecular Orientation and Spontaneous Interfacial Mixing on the Performance of Organic Solar Cells 2015:150728150637001 Chemistry of Materials
Publisher:
American Chemical Society (ACS)
Journal:
Chemistry of Materials
Issue Date:
28-Jul-2015
DOI:
10.1021/acs.chemmater.5b01845
Type:
Article
ISSN:
0897-4756; 1520-5002
Additional Links:
http://pubs.acs.org/doi/abs/10.1021/acs.chemmater.5b01845
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Solar and Photovoltaic Engineering Research Center (SPERC)

Full metadata record

DC FieldValue Language
dc.contributor.authorNgongang Ndjawa, Guy Olivieren
dc.contributor.authorGraham, Kennethen
dc.contributor.authorLi, Ruipengen
dc.contributor.authorConron, Sarah Men
dc.contributor.authorErwin, Patricken
dc.contributor.authorChou, Kang Weien
dc.contributor.authorBurkhard, Georgeen
dc.contributor.authorZhao, Kuien
dc.contributor.authorHoke, Eric T.en
dc.contributor.authorThompson, Mark Een
dc.contributor.authorMcGehee, Michael D.en
dc.contributor.authorAmassian, Aramen
dc.date.accessioned2015-08-02T13:53:14Zen
dc.date.available2015-08-02T13:53:14Zen
dc.date.issued2015-07-28en
dc.identifier.citationImpact of Molecular Orientation and Spontaneous Interfacial Mixing on the Performance of Organic Solar Cells 2015:150728150637001 Chemistry of Materialsen
dc.identifier.issn0897-4756en
dc.identifier.issn1520-5002en
dc.identifier.doi10.1021/acs.chemmater.5b01845en
dc.identifier.urihttp://hdl.handle.net/10754/561612en
dc.description.abstractA critically important question that must be answered to understand how organic solar cells operate and should be improved is how the orientation of the donor and acceptor molecules at the interface influences exciton diffusion, exciton dissociation by electron transfer and recombination. It is exceedingly difficult to probe the orientation in bulk heterojunctions because there are many interfaces and they are arranged with varying angles with respect to the substrate. One of the best ways to study the interface is to make bilayer solar cells with just one donor-acceptor interface. Zinc phthalocyanine is particularly interesting to study because its orientation can be adjusted by using a 2-nm-thick copper iodide seed layer before it is deposited. Previous studies have claimed that solar cells in which fullerene acceptor molecules touch the face of zinc phthalocyanine have more current than ones in which the fullerenes touch the edge of zinc phthalocyanine because of suppressed recombination. We have more thoroughly characterized the system using in situ x-ray photoelectron spectroscopy and found that the interfaces are not as sharp as previous studies claimed when formed at room temperature or above. Fullerenes have a much stronger tendency to mix into the face-on films than into the edge-on films. Moreover we show that almost all of the increase in the current with face-on films can be attributed to improved exciton diffusion and to the formation of a spontaneously mixed interface, not suppressed recombination. This work highlights the importance of spontaneous interfacial molecular mixing in organic solar cells, the extent of which depends on molecular orientation of frontier molecules in donor domains.en
dc.language.isoenen
dc.publisherAmerican Chemical Society (ACS)en
dc.relation.urlhttp://pubs.acs.org/doi/abs/10.1021/acs.chemmater.5b01845en
dc.rightsThis document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemistry of Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.chemmater.5b01845.en
dc.titleImpact of Molecular Orientation and Spontaneous Interfacial Mixing on the Performance of Organic Solar Cellsen
dc.typeArticleen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentSolar and Photovoltaic Engineering Research Center (SPERC)en
dc.identifier.journalChemistry of Materialsen
dc.eprint.versionPost-printen
dc.contributor.institutionDepartment of Materials Science and Engineering, Stanford University, Stanford, California 94305, United Statesen
dc.contributor.institutionCornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, NY, 14850, United Statesen
dc.contributor.institutionDepartment of Chemistry, University of Southern California, Los Angeles, California 90089, United Statesen
dc.contributor.affiliationKing Abdullah University of Science and Technology (KAUST)en
kaust.authorGraham, Kennethen
kaust.authorZhao, Kuien
kaust.authorAmassian, Aramen
kaust.authorNgongang Ndjawa, Guy Olivieren
kaust.authorLi, Ruipengen
kaust.authorChou, Kang Weien
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