We present a theoretical and experimental study of carrier injection across organic heterojunctions of various barrier heights (0.4–1.0 eV) over a wide range of temperatures. An injection model with proposed escape probability function is formulated to include the total hopping frequencies at both sides of the heterojunction. The model predicts that the injection current at low temperature can be dramatically modified by an extremely small amount of deep trap states. More importantly, the temperature dependence of the injection current is found to decrease with increasing the barrier height. This suggests that extracting the barrier height from the versus 1/T plot, as commonly employed in literature, is problematic. Experimentally, hole-only heterojunction devices with injection barrier from 0.4 to 1.0 eV were fabricated by using various organic materials. -tris(N-3-methylphenyl-N-phenyl-amino) triphenylamine was chosen as the injecting layer. The accepting layer was -diphenyl--bis(1-naphthyl)(-biphenyl)--diamine, tris(8-hydroxyquinoline) aluminum (Alq), -tris(N-carbazolyl)-triphenylamine, or -(1,3,5-phenylene) tris(1-phenyl-1H-benzimidazole). The measured electric field and temperature dependence of the injection currents of the heterojunction devices were in good agreement with the calculation results.
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15 January 2011
Research Article|
January 19 2011
Temperature dependence of carrier injection across organic heterojunctions
S. W. Tsang;
S. W. Tsang
a)
1Department of Material Science and Engineering,
University of Toronto
, Toronto, Ontario M5S 3E4, Canada
2Institute for Microstructural Sciences,
National Research Council of Canada
, Ottawa, Ontario K1A 0R6, Canada
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Y. Tao;
Y. Tao
2Institute for Microstructural Sciences,
National Research Council of Canada
, Ottawa, Ontario K1A 0R6, Canada
Search for other works by this author on:
a)
To whom correspondence should be addressed. Electronic mail: sai-wing.tsang@cnrc-nrc.gc.ca.
b)
Electronic mail: zhenghong.lu@utoronto.ca.
J. Appl. Phys. 109, 023711 (2011)
Article history
Received:
August 21 2010
Accepted:
December 02 2010
Citation
S. W. Tsang, Y. Tao, Z. H. Lu; Temperature dependence of carrier injection across organic heterojunctions. J. Appl. Phys. 15 January 2011; 109 (2): 023711. https://doi.org/10.1063/1.3536530
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