Mobility enhancement through homogeneous nematic alignment of a liquid-crystalline polyfluorene

Abstract

Homogeneous alignment of poly(9,9′-dioctylfluorene) films on rubbed polyimide results in a more than one order of magnitude increase in time-of-flight hole mobility normal to the alignment direction. We find μ=8.5±1×10−3 cm2/V s at an electric field of E=104 V/cm. Hole transport is found to be nondispersive, indicating a low degree of energetic disorder.

Charge transport in disordered organic solids: A Monte Carlo simulation study on the effects of film morphology

“…In these models of charge transport the influence of film morphology of the active layers, which has profound effects on charge transport, is not considered well. The presence of ordered regions can in-fact reduce the overall energetic disorder in the material [9,16] that can enhance the mobility and at the same time can substantially influence the behavior of charge transport [17][18][19][20]. The presence of structural order can change the mechanism of charge transport drastically because it may be possible that in ordered regions the charge transport may be of the band type and hence the overall mechanism may be a combination of the band and the hopping transport [21].…”

“…The presence of structural order can change the mechanism of charge transport drastically because it may be possible that in ordered regions the charge transport may be of the band type and hence the overall mechanism may be a combination of the band and the hopping transport [21]. Field dependence of mobility in partially ordered samples generally shows a Poole-Frenkel type behavior [22][23][24][25] but in some cases either very weak field dependence or even negative field dependence, at low temperatures, of mobility have been observed [16,18,22,26,27]. Temperature dependence of mobility in these partially ordered films has also been a matter of discussion whether logμ follows 1/T or 1/T 2 .…”

Structure, photophysics, and the order-disorder transition to theβphase in poly(9,9-(di-n,n-octyl)fluorene)

“…Poly(9,9-(di n,n-octyl)fluorene), or PF8 as schematically shown in Fig. 1, has received extra attention because it exhibits mesomorphic behavior and multiple crystal phases 13,14,15,16,17 . On heating of PF8 thin films one generally observes transitions from a crystalline state to a liquid crystalline mesophase followed by melting R = (CH 2 7 ) +CH 3 8. to an isotropic phase.…”

<i>In-Situ</i> Measurements of the Photoconductivity of Multi-Layered Organic Photovoltaic Devices Using Impedance Spectroscopy

“…Along with IS measurements, other methods have been used to measure the mobility in highly resistive organic semiconductor films and other materials including the time-of-flight (TOF) method [10] [11], the dark injection (DI) transient method [12]- [15], a method to obtain the mobility from the I-V characteristics of the space charge limited current (SCLC), time-resolved electroluminescence (EL) spectroscopy [16] and the photoexcited time-resolved microwave conductivity technique [17] [18]. To accurately evaluate the transit time using the TOF and DI methods, a film that is substantially thicker than the light-emitting layer in an organic EL device is required.…”