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Extraction of the materials parameters that determine the mobility in disordered organic semiconductors from the current-voltage characteristics: Accuracy and limitations
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10.1063/1.4795588
/content/aip/journal/jap/113/11/10.1063/1.4795588
http://aip.metastore.ingenta.com/content/aip/journal/jap/113/11/10.1063/1.4795588

Figures

Image of FIG. 1.
FIG. 1.

Schematic energy level diagram of a double-carrier device indicating all materials and device parameters included in this study. For holes ( and electrons ( ), the widths of the DOS, , the hopping site distances , and the injection barriers Δ at the anode (A) and cathode (C) are indicated. For the electrons, the superimposed exponential DOS is indicated with the two additional parameters involved, E 0 and . An applied voltage (V) leads to an energy difference between the Fermi levels ( ) of the anode and the cathode.

Image of FIG. 2.
FIG. 2.

J(V, L, T) characteristics, generated using the ECDM with 10% noise in J ( ), obtained from a fit using the ECDM (solid lines) and obtained from a fit using the EGDM (dashed lines), for an organic layer thickness equal to 67 nm (a) and 122 nm (b) and for a temperature equal to 272, 220, and 170 K. The parameter values used for generating the curves are given in the text.

Image of FIG. 3.
FIG. 3.

Results of the ECDM and EGDM analyses presented in Sec. III A . (Un)converged results are indicated by open (filled) symbols. The plus symbols indicate the initial parameter values. (a) Sequences of -values as obtained using the ECDM ( ) and the EGDM ( and ), in the latter case resulting from two different starting points. (b) Trajectories in the -plane corresponding to the sequences shown in Figure 3(a) . (c) Temperature dependence of (symbols) and best fits based on Eq. (7) (solid lines). (d) Projection of the full 95% confidence ellipsoid on the -plane.

Image of FIG. 4.
FIG. 4.

Fit parameters (open symbols) obtained using the EGDM and the ECDM for J(V) curves generated using the other model and using the initial σ and parameter values indicated by the solid symbols. The calculations were carried out for 100 nm thick devices assuming T = 273 K. The other initial parameters are given in the text.

Image of FIG. 5.
FIG. 5.

Effect on the -value as obtained from the ECDM analysis presented in Sec. III B when constraining some of the parameter values. Solid square: end-point of the extraction procedure. Full (dashed) curves: (σ)-curve around the best fit σ-value as predicted using Eq. (2) without (with) constraints. Crosses: -values obtained from the actual model calculations using the predicted optimal values (Eq. (2) ) of all non-constrained parameters. Solid spheres: -values, obtained from the re-application of the parameter extraction method while constraining σ and all other parameter values specified. Open spheres: intermediate (non-converged) results. (a) All parameters free, except σ. The arrow indicates that the value of the upper datapoint (cross) at σ = 0.11 eV is actually far outside the frame of the figure, viz. at . (b) All parameters constrained, except for the mobility parameters . (c) All parameters free, except σ and . Arrow: see full text.

Image of FIG. 6.
FIG. 6.

Obtained best fit -values as a function of the width of the density of states σ, for the case studied in Sec. IV B . The uncertainty margins of every point and a guide-to-the eye (drawn curve) are shown.

Image of FIG. 7.
FIG. 7.

Obtained best-fit parameters as a function of the width of the density of states, σ, for the case studied in Sec. IV B , for (a) the site density, (b) the trap site density, (c) the trap width, (d) the built-in voltage, and (e) the C parameter, defined by Eq. (7) .

Image of FIG. 8.
FIG. 8.

Obtained best-fit temperature-dependent values of the mobility, , for three different values of σ (symbols), linear fits to data (lines), and the values of the slope parameters C (defined by Eq. (7) ).

Image of FIG. 9.
FIG. 9.

Histogram of the measured current density at 273 K and at 5 V for a hole-only PF-TAA based device with a layer thickness of 122 nm, as discussed in Sec. IV A . The solid line shows the best-fit normal distribution.

Image of FIG. 10.
FIG. 10.

Voltage dependence of the standard deviation of the measured current density for two temperatures (295 K and 273 K) in a PF-TAA based hole-only device with a layer thickness of 122 nm, as discussed in Sec. IV A .

Tables

Generic image for table
Table I.

Overview of the cases studied in this paper. The description indicates which of the elements, shown in Figure 1 , are included. A = artificial data and E = experimental data.

Generic image for table
Table II.

Initial and obtained parameter values for the ECDM data sets studied in Secs. III A and III B , analyzed using the ECDM model. A trap DOS, characterized by the parameters and E 0 (see text), was only assumed in Sec. III B .

Generic image for table
Table III.

EGDM parameter values describing the current density in the PF-TAA based hole-only devices discussed in Sec. IV A , as obtained in Ref. 8 and as obtained in this paper. As in Ref. 8 , was taken. For the 67 and 122 nm devices, slightly different values of were found in both studies.

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/content/aip/journal/jap/113/11/10.1063/1.4795588
2013-03-19
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Extraction of the materials parameters that determine the mobility in disordered organic semiconductors from the current-voltage characteristics: Accuracy and limitations
http://aip.metastore.ingenta.com/content/aip/journal/jap/113/11/10.1063/1.4795588
10.1063/1.4795588
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