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    Effect of a large hole reservoir on the charge transport in TiO2/organic hybrid devices

    Year: 2012

    Journal: Phys. Chem. Phys., 2012, 14 (41), 14186-14189, 20131009

    Authors: Simon Sandén, Oskar Sandberg, Qian Xu, Jan-Henrik Smått, Gytis Juška, Mika Lindén, Ronald Österbacka

    Organizations: Department of Natural Sciences, Physics and Center of Functional Materials, Åbo Akademi University, Porthansgatan 3, 20500, Åbo, Finland; Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan; Department of Natural Sciences, Laboratory of Physical Chemistry and Center of Functional Materials, Åbo Akademi University, Porthansgatan 3, 20500, Åbo, Finland; Department of Solid State Electronics, Vilnius University, Saul_etekio 9, 10222 Vilnius, Lithuania; Institute of Inorganic Chemistry II, The University of Ulm, Albert-Einstein-Alle 11, 89081 Ulm, Germany

    We have fabricated hybrid devices in the form of indium tin oxide/titanium dioxide/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/copper (ITO/TiO2/P3HT:PCBM/Cu) to clarify the impact of the TiO2/P3HT:PCBM interface on the charge transport using the charge extraction by linearly increasing voltage (CELIV) technique. We found that a large equilibrium charge reservoir is accumulated at negative offsets at the TiO2/P3HT:PCBM interface leading to space charge limited extraction current (SCLC) transients. We show analytically the SCLC transient response and compare the experimental data to calculated SCLC at a linearly increasing voltage. The theoretical calculations indicate that the large charge reservoir at negative offset voltages is due to thermally generated charges combined with poor hole extraction at the ITO/TiO2 contact, due to the hole blocking character of TiO2.