Thin air-plasma-treated alkali fluoride layers for improved hole extraction in copper phthalocyanine/C70-based solar cells

Teng Xiao; Weipan Cui; Ruth Shinar; Min Cai; Rui Liu; James W. Anderegg; Joseph Shinar

doi:10.1117/1.JPE.2.021006

12 March 2012 Thin air-plasma-treated alkali fluoride layers for improved hole extraction in copper phthalocyanine/C₇₀-based solar cells

Teng Xiao, Weipan Cui, Ruth Shinar, Min Cai, Rui Liu, James W. Anderegg, Joseph Shinar

Author Affiliations +

Journal of Photonics for Energy, Vol. 2, Issue 1, 021006 (March 2012). https://doi.org/10.1117/1.JPE.2.021006

Abstract

Alkali fluorides, mostly LiF and CsF, are well-known to improve electron injection/extraction in organic light-emitting diodes (OLEDs) and organic solar cells (OSCs). They are also utilized, though to a lesser extent, for hole injection in OLEDs. Here we demonstrate a new role for such fluorides in enhancing OSCs' hole extraction. We show that an ultrathin air-plasma-treated alkali fluoride layer between the indium tin oxide (ITO) anode and the active layer in copper phthalocyanine (CuPc)/C70-based OSCs increases the short circuit current by up to ∼ 17% for cells with LiF and ∼ 7% for cells with NaF or CsF. The effects of the fluoride layer thickness and treatment duration were evaluated, as were OSCs with oxidized and plasma-treated Li and UV-ozone treated LiF. Measurements included current voltage, absorption, external quantum efficiency (EQE), atomic force microscopy, and x-ray photoelectron spectroscopy, which showed the presence of alkali atoms F and O at the treated ITO/fluoride surface. The EQE of optimized devices with LiF increased at wavelengths >560 nm, exceeding the absorption increase. Overall, the results indicate that the improved performance is due largely to enhanced hole extraction, possibly related to improved energy-level alignment at the fluorinated ITO/CuPc interface, reduced OSC series resistance, and in the case of LiF, improved absorption.

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Teng Xiao, Weipan Cui, Ruth Shinar, Min Cai, Rui Liu, James W. Anderegg, and Joseph Shinar "Thin air-plasma-treated alkali fluoride layers for improved hole extraction in copper phthalocyanine/C₇₀-based solar cells," Journal of Photonics for Energy 2(1), 021006 (12 March 2012). https://doi.org/10.1117/1.JPE.2.021006

Published: 12 March 2012

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