Trap-controlled hole transport in small molecule organic semiconductors

Abstract

The influence of trap concentration on hole transport is investigated by an optical time-of-flight method for the amorphous small molecule organic semiconductor N,N′-bis(1-naphtyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamin (α-NPD) doped with neutral hole traps by codeposition of 4,4′,4″-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA). α-NPD doped with 120ppm 1-NaphDATA exhibits nondispersive hole transport like undoped α-NPD, but trap-controlled with reduced mobility. The trap depth derived from the mobility decrease coincides with the ionization potential difference of α-NPD and 1-NaphDATA. The transition to dispersive transport for increasing trap concentration to 1160ppm is explained by an energetic relaxation of optically generated charge carriers within a density of states broadened by traps.

The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

“…The extracted values are in qualitative agreement with values reported earlier in the literature: the reported hole mobilities in a-NPD using time-of-flight lie in the range of 3-9 Â 10 À4 cm 2 /Vs, [47][48][49][50][51][52] However, as a side remark we want to note that, instead of using CELIV formulas, we can also resort to driftdiffusion simulations as we have already demonstrated in the context of OSCs. 30,40 Since in the MIS-regime of the polar device only holes are present, the CELIV transients can be fitted with the hole mobility as the only fitting parameter.…”

Transit Phenomena in Organic Field‐Effect Transistors Through Kelvin‐Probe Force Microscopy

“…In amorphous ZnPC the density dependence was less pronounced. Assuming the Gaussian disorder model, the presence of trap states results in a larger effective disorder parameter as was demonstrated earlier 14. Hence, a trap‐state broadened, effective disorder parameter at low carrier densities in polycrystalline pentacene films is possible going along with the pronounced carrier‐density dependence of the hole mobility.…”

Trapping-detrapping fluctuations in organic space-charge layers

“…The agreement between theory and experiments validates the model and provides an estimate of the concentration and energy level of deep traps.Polymeric as well as small molecular semiconductor electronic products have shown impressive improvements in their performance during recent years. Organic field-effect transistors (OFETs) and light-emitting diodes (OLEDs), solar cells and memories successfully compete with traditional electronic devices when flexibility, large area, low cost and weight are the main requirements [1][2][3]. The injection of charge carriers at molecule-metal interfaces plays a decisive role in the performance of organic semiconductor devices.…”