Effect of dipoles on carrier drift and diffusion of molecularly doped polymers

Effect of dipolar molecules on carrier mobilities in photorefractive polymers

“…͑5͒ for a doped polymer containing a strong dipolar additive in addition to a polar charge transport agent. The data are more consistent with the linear dependence on concentration, n ϭ1, proposed by Young 35 and Dunlap, Parris, and Kenkre, 38 while the superlinear dependence, 2nϭ4/3, of Dieckman, Bässler, and Borsenberger 36 and Hirao and Nishizawa 37 would be too strong. The NAS chromophores have a larger effect on the energy width despite having a smaller dipole moment ͑6.7 D͒ than EHDNPB ͑7.6 D͒, but EHDNPB is much larger because of its alkyl tail ͓see Fig.…”

“…[28][29][30][31][32][33][34] The dipolar effect on charge transport in doped polymers has been described in a qualitative manner by a model based on dipolar disorder. 28,30 The more quantitative descriptions can be found in later work, where the random potentials due to the electric fields of the dipoles are incorporated into the Gaussian disorder model, [35][36][37] or derived from a one-dimensional random potential model. 38 The main argument of the dipolar disorder model is that the local variation of the electrostatic potential resulting from randomly distributed and oriented dipoles increases the width of the Gaussian energy distribution.…”

“…The total energy width includes the dipolar contribution d in addition to the usual van der Waals contribution vdw . The two contributions are assumed statistically independent and are therefore combined in quadrature 28 8,9,11,[29][30][31][32]37,39,40 but there are some studies that appear to contradict this form. 33,41,42 The observation of mobility reduction by dipolar disorder in molecularly doped polymers underlines the importance of similar studies of charge transport in photorefractive polymers, which necessarily contain large concentrations of polar nonlinear chromophores.…”

Полевая Диффузия В Неупорядоченных Органических Материалах В Условиях Заполнения Глубоких Состояний

“…Известно, что сигнал переходного тока, наблюдаемый в экспериментах по измерению времени пролета, имеет аномально широкий участок убывания при временах, превышающих время пролета, даже если до времени пролета наблюдается участок постоянства тока, так что постоянное значение подвижности успело устано-виться [1,3]. Во многих случаях, наблюдаемый сигнал может быть описан на основе уравнения непрерывности, которое включает не зависящие от времени подвижность и коэффициент диффузии, но последний оказывается много больше, чем следует из известного соотношения Эйнштейна [1][2][3][4][5]. Таким образом, дисперсия (разброс координат) дрейфующего пакета носителей заряда ано-мально велика, несмотря на отсутствие дисперсионного транспорта [1].…”

Improved efficiency of blue phosphorescence organic light‐emitting diodes with irregular stepwise‐doping emitting layers

“…The hole transport from NPB to TCTA is favorable, since highest occupied molecular orbitals (HOMO) difference between NPB (HOMO: 5.4 eV) [17] and TCTA (HOMO: 5.7 eV) [17] is only 0.3 eV. Though the HOMO level difference between TCTA and FIrpic (HOMO: 5.9 eV) [17] is small (0.2 eV), the hole drift mobility is reduced by increasing FIrpic doping concentration, due to the energetic disorder [18]. On the other hand, the electron transporting direct from BPhen to TCTA is unlikely due to large lowest unoccupied molecular orbitals (LUMO) mismatch (0.6 eV) [17].…”