Spectroscopic Imaging of Photopotentials and Photoinduced Potential Fluctuations in a Bulk Heterojunction Solar Cell Film

Luria, J.L.; Hoepker, N.; Bruce, R.; Jacobs, A.R.; Groves, C.; Marohn, J.A.

Abstract

We present spatially resolved photovoltage spectra of a bulk heterojunction solar cell film composed of phase-separated poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB) polymers prepared on ITO/PEDOT:PSS and aluminum substrates. Over both PFB- and F8BT-rich domains, the photopotential spectra were found to be proportional to a linear combination of the polymers’ absorption spectra. Charge trapping in the film was studied using photopotential fluctuation spectroscopy, in which low-frequency photoinduced electrostatic potential fluctuations were measured by observing noise in the oscillation frequency of a nearby charged atomic force microscope cantilever. Over both F8BT- and PFB-rich regions, the magnitude, distance dependence, frequency dependence, and illumination wavelength dependence of the observed cantilever frequency noise are consistent with photopotential fluctuations arising from stochastic light-driven trapping and detrapping of charges in F8BT. Taken together, our findings suggest a microscopic mechanism by which intermixing of phases leads to charge trapping and thereby to suppressed open-circuit voltage and decreased efficiency in this prototypical bulk heterojunction solar cell film.

Citation

Luria, J., Hoepker, N., Bruce, R., Jacobs, A., Groves, C., & Marohn, J. (2012). Spectroscopic Imaging of Photopotentials and Photoinduced Potential Fluctuations in a Bulk Heterojunction Solar Cell Film. ACS Nano, 6(11), 9392-9401. https://doi.org/10.1021/nn300941f

• Journal Article Type: Article
• Acceptance Date: Oct 2, 2012
• Online Publication Date: Oct 8, 2012
• Publication Date: Nov 27, 2012
• Deposit Date: Dec 3, 2012
• Journal: ACS Nano
• Print ISSN: 1936-0851
• Electronic ISSN: 1936-086X
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 6
• Issue: 11
• Pages: 9392-9401
• DOI: https://doi.org/10.1021/nn300941f
• Keywords: PFB, P8BT solar cell, Open-circuit voltage, Scanning Kelvin probe microscopy, Photovoltage and photopotential fluctuation spectroscopy.
• Public URL: https://durham-repository.worktribe.com/output/1468463