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    Influence of equilibrium charge reservoir formation on photo generated charge transport in TiO2/organic devices

    Year: 2014

    Journal: ORGANIC ELECTRONICS, Vol. 15, p 3506-3513, 20150722

    Authors: Sanden, S.; Sandberg, O. J.; Xu, Q.; Smatt, J. -H.; Juska, G.; Linden, M.; Osterbacka, R.

    Organizations: Abo Akad Univ, Dept Nat Sci, Turku 20500, Finland; Abo Akad Univ, Ctr Funct Mat, Turku 20500, Finland; Abo Akad Univ, Finnish Natl Doctoral Programme Nanosci NGS NANO, Turku 20500, Finland; Abo Akad Univ, Dept Nat Sci, Phys Chem Lab, Turku 20500, Finland; Vilnius State Univ, Dept Solid State Elect, LT-10222 Vilnius, Lithuania; Univ Ulm, Inst Inorgan Chem 2, D-89081 Ulm, Germany

    Charge transport measurements have been performed using the photo induced charge extraction by linearly increasing voltage (photo-CELIV) technique on indium tin oxide/titanium dioxide/ poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/copper (ITO/TiO2/P3HT:PCBM/Cu) devices. By adjusting the offset voltage such that holes are accumulated at the ITO/TiO2 contact we obtain space charge limited current (SCLC) extraction in the dark. Using photo-generation the current response is limited by SCLC extraction at low carrier concentrations but becomes purely recombination limited at high photo-generated carrier concentration. A 1-D drift diffusion model has been developed to simulate our results and we show that the hole blocking ITO/TiO2 contact is responsible for the SCLC behavior. The highly reduced recombination of charges seen in P3HT: PCBM devices is necessary to obtain the large extraction current transients that are seen in the experimental measurements. By comparing the simulated dark CELIV and photo-CELIV we show that photo-generated extraction is more sensitive towards changes in the surface recombination velocity. (C) 2014 Elsevier B.V. All rights reserved.