ИСТИНА

The most popular model for simulation of organic electronic devices describes charge transport using drift-diffusion equations. Particular features of the transport in organic materials (mostly, polymers) are taken into account by empirical formulas describing mobility field, temperature, and concentration dependence [1,2]. Discrete trap energy [3] or an exponential trap distribution [4] are extensively used. However, according to [5] the charge transport in thin polymer films could be non-equilibrium, thus rendering the drift-diffusion approach inapplicable. In reality, trap distribution may differ significantly from both an exponential or the Gaussian one. In fact, even a usual assumption of spatially uncorrelated trap distribution is under suspicion in organic materials [6]. We provide theoretical description of charge transport in polymers using the MTM with an arbitrary trap distribution (treatment of the Gaussian distribution is based on the earlier paper [7]). Experimental transport data have been obtained using the time-of-flight technique, while the parameters of the charge generation and recombination processes have been obtained using the radiation induced conductivity measurements. We also report experimental and theoretical results on the influence of immobile charged centers on the time-of-flight transients in molecularly doped polymers. In addition, we show how to incorporate results of the Monte-Carlo simulations of charge transport and recombination processes into the MTM [8]. If there is no need to take into account the effects of the non-equilibrium electronic transport, we show how the MTM could be reduced to the drift-diffusion model with usual Poole-Frenkel mobility field dependence and its temperature dependence lnµ~-1/T², integrated in the model [9]. Suggested approach has been used to calculate current-voltage characteristics of organic bulk heterojunction solar cell. References [1] Knapp, E.; Ruhstaller, B. "Numerical analysis of steady-state and transient charge transport in organic semiconductor devices". Optical and Quantum Electronics. 42, 667-677 (2011). [2] Rubel, O.; Baranovskii, S.; Thomas, P.; Yamasaki, S. "Concentration dependence of the hopping mobility in disordered organic solids". Phys. Rev. B. 69, 014206 (2004). [3] Hwang, I.; McNeill, C.; Greenham, N. "Drift-diffusion modeling of photocurrent transients in bulk heterojunction solar cells". J. Appl. Phys. 106, 094506 (2009). [4] Christ, N.; Kettlitz, S.; Zufle, S.; Valouch, S.; Lemmer U. "Nanosecond response of organic solar cells and photodiodes: role of trap states". Phys. Rev. B. 83, 195211 (2011). [5] Nikitenko, V.; von Seggern, H.; Bässler H. "Non-equilibrium transport of charge carriers in disordered organic materials" J. Phys.: Condensed Matter. 19, 136210 (2007). [6] Novikov, S. "Charge-carrier transport in disordered polymers". J. Polymer Science B. 41, 2584 (2011). [7] Tyutnev, À.; Ikhsanov, R; Saenko, V.; Pozhidaev, E. "Analysis of the time-of-flight transients in molecularly doped polymers using the Gaussian disorder model". J. Phys.: Condensed Matter. 23, 325105 (2011). [8] Korolev, N.; Nikitenko, V.; Ivanov, D. "Quasi-equilibrium hopping drift and field-stimulated diffusion in very thin layers of organic materials". Semiconductors, v.45, ¹2, 230-235(2011). [9] Tyutnev, À.; Saenko, V.; Pozhidaev, E.; Kostyukov N. "Dielectric properties of polymers in ionizing radiation fields". M.: Nauka (in Russian), (2005).