Sano-Tachiya-Noolandi-Hong versus Onsager modelling of charge photogeneration in organic solids |
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Authors: | K. Falkowski W. Stampor P. GrygielW. Tomaszewicz |
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Affiliation: | a Department of Electronic Phenomena, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Narutowicza 11/12, 80-233 Gdańsk, Poland b Department of Atomic Physics and Luminescence, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Narutowicza 11/12, 80-233 Gdańsk, Poland |
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Abstract: | We have studied the electric field dependence of charge photogeneration efficiency in organic solids for various radial distribution functions (Dirac delta, Gaussian, exponential) of initial e-h pairs in the framework of Sano-Tachiya-Noolandi-Hong (STNH) theory assuming that the final recombination (capture reaction) proceeds on a sphere of finite radius (a) with a finite velocity (κ). We compare the STNH results with the conventional Onsager theory assuming a = 0. We show that charge photogeneration is more enhanced, especially in low-electric field range, for broader initial pair distributions and for smaller final recombination velocities. We compare theoretical results with experimental data taken from electromodulation of photoluminescence (EML) for two archetypical organic photoconductors, Alq3 and Ir(ppy)3, commonly used as emitters in organic LEDs. From analysis of our results we infer the lower limit of final recombination velocity, κ = 0.2-2 cm/s, in vacuum evaporated films of Alq3 and Ir(ppy)3 which compares favorably with an evaluation of this quantity in amorphous solids. |
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Keywords: | Charge photogeneration Onsager model Geminate recombination Organic solids Electromodulation OLEDs Alq3 Iridium complex |
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