The impact of controlled solvent exposure on the morphology, structure and function of bulk heterojunction solar cells

Raghavendra Hegde, Nathan Henry, Ben Whittle, Huidong Zang, Bin Hu, Jihua Chen, Kai Xiao, Mark Dadmun

Research output: Contribution to journalArticlepeer-review

50 Scopus citations

Abstract

Films of poly(3-hexyl thiophene) (P3HT):[6,6]-phenyl C 61-butyric acid methyl ester (PCBM) were controllably exposed to CS 2 vapor in a column with a linear solvent vapor pressure gradient. Changes in the morphology of the P3HT:PCBM thin film were monitored and correlated to the ability of this thin film to act as the active layer in an organic solar cell. The results show that the crystallinity and crystal size of the P3HT increase initially with solvent vapor pressure and annealing time, but longer exposure to solvent decreases P3HT crystallinity and photovoltaic efficiency. Neutron reflectivity indicates that the PCBM segregates to the Si substrate in the as-cast thin film, but distributes throughout the film with solvent annealing. The changes in crystallinity and the depth profile of the P3HT:PCBM mixture differ from those induced by thermal annealing. The structural variation with solvent exposure is correlated to photovoltaic function, demonstrating that the solvent annealing provides a window of optimum efficiency, which depends on solvent exposure. Moreover, the control of depth profile and structure should be generally applicable to a broad range of polymer-nanoparticle mixtures and thus these results provide fundamental information that can be used to control the depth profile, morphology and function of thin film nanocomposites.

Original languageEnglish
Pages (from-to)112-124
Number of pages13
JournalSolar Energy Materials and Solar Cells
Volume107
DOIs
StatePublished - Dec 2012

Funding

The authors wish to acknowledge financial support from the National Science Foundation ( CBET-0932666 ), as well as the support of the Sustainable Energy Education Research Center at the University of Tennessee. We acknowledge the support of the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy, who sponsors the Spallation Neutron Source (SNS), the SHaRE User Facility, and the Center for Nanophase Materials Sciences (CNMS) at Oak Ridge National Laboratory. The authors acknowledge a DOE Laboratory Directed Research and Development (LDRD) award (#5388). We are grateful to Dr. John Ankner for providing m-layer fitting software for neutron reflectivity data. We also thank Dr. Joseph E. Spruiell for assistance with GIWAXS measurements. Appendix A

FundersFunder number
CNMS
Center for Nanophase Materials Sciences
Spallation Neutron Source
Sustainable Energy Education Research Center
US Department of Energy
Basic Energy Sciences
Oak Ridge National Laboratory
Laboratory Directed Research and Development5388
University of Tennessee
Scuola Normale Superiore
National Science FoundationCBET-0932666

    Keywords

    • Crystallinity
    • Depth profile
    • Morphology
    • Organic solar cell
    • Solvent annealing

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