A metrology perspective on the dark injection transient current method for charge mobility determination in organic semiconductors

Abstract

Charge mobility is a key parameter for understanding the performance of organic semiconductor devices and materials. A range of techniques is available that can measure charge mobility with varying accuracy and precision. In this paper we analyze the dark injection transient current (DITC) method from a metrology perspective. We carried out a systematic study of the sensitivity of single carrier analogues of organic light-emitting diodes (OLEDs) to small changes in electrical input and environmental conditions. We observed that the experimental results depend strongly on the previous history of the device under test, with both long term and short term effects in evidence. Our findings demonstrate the need for caution in interpreting the results of single experiments to determine the charge mobility of OLEDs and the difficulty of associating uncertainty statements with the results of charge mobility measurements.

The role of shallow traps in dynamic characterization of organic semiconductor devices

“…Further, we have used our model with charge traps for DITC simulations, and it is able to reproduce the slow decay of the current peak and the shift of the peak position as commonly observed in DITC experiments such as presented in Ref. 20. This extended model is thus capable of generating more realistic current transients and may help to reveal crucial parameters of charge traps such as density, energetic depth, and the capture coefficient.…”

“…In Ref. 20, a systematic study on the sensitivity of single carrier transport to changes in the applied voltage pulse is performed. Experimental parameters such as the pulse amplitude, on-time, off-time, and the ambient temperature were varied.…”

“…With the trap kinetics in the numerical model, we found a suitable and convincing explanation for the observed relaxation effects in DITC measurements in OLEDs. 20…”

“…While Ref. 4 claims that DITC is the most suitable method for thin samples, Esward et al 20 have pointed out that dark injection transient current measurements of OLEDs are sensitive to a range of experimental parameters such as pulse on-and off-times. So far, the charge mobility values have been extracted from the current response measurements 1,4,18,19 by the formula l ¼ 0:…”

Techniques for characterization of charge carrier mobility in organic semiconductors

“…48 DI SCLC technique has also been utilized to determine the hole mobilities of polyfluorene copolymers. [49][50][51] The authors also reported that pretreatment of Indium tin oxide (ITO) and PEDOT-PSS with O 2 plasma aided in obtaining the desired DI current transients.…”