Analysis and modeling of organic devices

Abstract

We present self consistent picture of charge injection and transport in low mobility disordered organic based devices. We demonstrate the importance of accounting for charge density effects in both modeling and analysis of devices. We outline a method for the analysis of LEDs and FETs.

Effect of Gaussian disorder on the voltage dependence of the current density in sandwich-type devices based on organic semiconductors

“…Roichman et al 10 were the first to include both effects of disorder on the mobility and the diffusion coefficient in a transport model for single-carrier sandwich-type devices. However, the model used in Ref.…”

“…However, the model used in Ref. 10 for quantifying the carrier density dependence of the mobility was shown to neglect the percolative nature of the hopping transport, 11 which strongly affects the temperature dependence of the mobility. Pasveer et al 12 developed a model that correctly includes the effects of percolation on the mobility and demonstrated that in the drift-dominated high-voltage regime the temperature dependence of the current density in PPV-based hole-only devices can be described well assuming Gaussian disorder.…”

“…In their device model, the diffusion contribution to the current density was neglected. Although the effects of diffusion have been included in inorganic semiconductor device models, 13 in models for OLEDs 10,14 and in models for other organic electronic devices, 15 so far in none of these studies the recent insights on the mobility in an organic semiconductor with Gaussian disorder, mentioned above, have been taken into account.…”

Effects of disorder on the current density and recombination profile in organic light-emitting diodes

“…This effect depends on the ratio of the width of the Gaussian DOS, , and the thermal energy, k B T, with k B the Boltzmann constant and T the temperature. [10][11][12] We will refer to the parametrization of the temperature, field, and density-dependent mobility as given by Pasveer et al, 11 based on the results of a master-equation ͑ME͒ study, as the "extended Gaussian disorder model" ͑EGDM͒. Successful quantitative descriptions of hole transport in paraphenylene-vinylene and polyfluorene-based sandwich-type devices, assuming a Gaussian DOS, were given by Pasveer et al 11 and Van Mensfoort et al, 13 respectively.…”

Analysis of hole transport in a polyfluorene-based copolymer— evidence for the absence of correlated disorder

“…Within their pioneering Monte Carlo studies of the effects of disorder on the mobility, Bässler 1 assumed an uncorrelated Gaussian distribution of hopping site energies. Pasveer et al 2 showed that an extension of their model to include a carrier density ͑n͒ dependence of the mobility, 3,4 leading to the "extended Gaussian disorder model" ͑EGDM͒, can well describe the temperature ͑T͒ dependent current-voltage characteristics ͓J͑V , T͔͒ of hole transport in sandwich-type devices based on polyphenylene-vinylene ͑PPV͒ polymers. A similar conclusion was recently obtained by van Mensfoort et al, 5 who analyzed the J͑V , T͒ characteristics of hole-only polyfluorene-based copolymer devices with various layer thicknesses L. The successful use of the EGDM mobility functions, 6 as obtained from a master-equation ͑ME͒ approach within which the nonequilibrium ͑"hot"͒ carrier energy distribution is calculated assuming a uniform carrier density and field, indicates that for the systems studied energy relaxation after injection of carriers in actual devices with nonuniform densities and fields takes place on a time scale that is much shorter than the transit time.…”