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Two-dimensional carrier distribution in top-gate polymer field-effect transistors: correlation between width of density of localized states and Urbach energy.

Kronemeijer AJ, Pecunia V, Venkateshvaran D, Nikolka M, Sadhanala A, Moriarty J, Szumilo M, Sirringhaus H - Adv. Mater. Weinheim (2013)

Bottom Line: A general semiconductor-independent two-dimensional character of the carrier distribution in top-gate polymer field-effect transistors is revealed by analysing temperature-dependent transfer characteristics and the sub-bandgap absorption tails of the polymer semiconductors.A correlation between the extracted width of the density of states and the Urbach energy is presented, corroborating the 2D accumulation layer and demonstrating an intricate connection between optical measurements concerning disorder and charge transport in transistors.

View Article: PubMed Central - PubMed

Affiliation: Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, United Kingdom.

No MeSH data available.


Related in: MedlinePlus

Normalized absorbance of spincoated polymer thin films measured by Photothermal Deflection Spectroscopy. Solid lines show fits to the exponential sub-bandgap regions using Eu equal to the extracted T0 values from the 2D FET model.
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fig04: Normalized absorbance of spincoated polymer thin films measured by Photothermal Deflection Spectroscopy. Solid lines show fits to the exponential sub-bandgap regions using Eu equal to the extracted T0 values from the 2D FET model.

Mentions: The slopes of the linear fits in the γ versus 1/T graphs yield the value of T0, the characteristic width of the (exponential) DOS. In order to verify the extracted T0 values we set out to obtain an additional independent measurement that is sensitive to the amount of disorder in the polymer films. In inorganic semiconductors, e.g., α-Si, disorder is known to result in the formation of states in the bandgap, broadening of the absorption onset and creating an exponential sub-bandgap absorption tail called the Urbach tail.16 The characteristic width of the exponential absorption tail Eu, i.e., the Urbach energy, has been shown to correlate with the amount of disorder in the material.17 In order to obtain the Urbach energies for the polymer semiconductors, we performed Photothermal Deflection Spectroscopy (PDS) on spincoated thin films. PDS is a sensitive spectroscopic technique able to accurately measure weak absorptions in the bandgap.18,19Figure4 shows the normalized PDS absorption spectra for the polymer films. All polymer films show an extended region below the bandgap where the absorption of the films decreases exponentially and from which values of the Urbach energy were extracted. A large error exists in the exact determination of the Urbach energy by virtue of the relatively arbitrary selection of the width of the exponential region to fit. Using different fitting procedures we have estimated the error in the determination of the Urbach energy. It is, nevertheless, possible to distinguish differences in the Urbach energies among the investigated polymers. N2200 has the sharpest bandtail while P3HT and PBTTT have significantly wider bandtails. This is consistent with the low degree of energetic disorder that has previously been reported for N2200.20


Two-dimensional carrier distribution in top-gate polymer field-effect transistors: correlation between width of density of localized states and Urbach energy.

Kronemeijer AJ, Pecunia V, Venkateshvaran D, Nikolka M, Sadhanala A, Moriarty J, Szumilo M, Sirringhaus H - Adv. Mater. Weinheim (2013)

Normalized absorbance of spincoated polymer thin films measured by Photothermal Deflection Spectroscopy. Solid lines show fits to the exponential sub-bandgap regions using Eu equal to the extracted T0 values from the 2D FET model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230477&req=5

fig04: Normalized absorbance of spincoated polymer thin films measured by Photothermal Deflection Spectroscopy. Solid lines show fits to the exponential sub-bandgap regions using Eu equal to the extracted T0 values from the 2D FET model.
Mentions: The slopes of the linear fits in the γ versus 1/T graphs yield the value of T0, the characteristic width of the (exponential) DOS. In order to verify the extracted T0 values we set out to obtain an additional independent measurement that is sensitive to the amount of disorder in the polymer films. In inorganic semiconductors, e.g., α-Si, disorder is known to result in the formation of states in the bandgap, broadening of the absorption onset and creating an exponential sub-bandgap absorption tail called the Urbach tail.16 The characteristic width of the exponential absorption tail Eu, i.e., the Urbach energy, has been shown to correlate with the amount of disorder in the material.17 In order to obtain the Urbach energies for the polymer semiconductors, we performed Photothermal Deflection Spectroscopy (PDS) on spincoated thin films. PDS is a sensitive spectroscopic technique able to accurately measure weak absorptions in the bandgap.18,19Figure4 shows the normalized PDS absorption spectra for the polymer films. All polymer films show an extended region below the bandgap where the absorption of the films decreases exponentially and from which values of the Urbach energy were extracted. A large error exists in the exact determination of the Urbach energy by virtue of the relatively arbitrary selection of the width of the exponential region to fit. Using different fitting procedures we have estimated the error in the determination of the Urbach energy. It is, nevertheless, possible to distinguish differences in the Urbach energies among the investigated polymers. N2200 has the sharpest bandtail while P3HT and PBTTT have significantly wider bandtails. This is consistent with the low degree of energetic disorder that has previously been reported for N2200.20

Bottom Line: A general semiconductor-independent two-dimensional character of the carrier distribution in top-gate polymer field-effect transistors is revealed by analysing temperature-dependent transfer characteristics and the sub-bandgap absorption tails of the polymer semiconductors.A correlation between the extracted width of the density of states and the Urbach energy is presented, corroborating the 2D accumulation layer and demonstrating an intricate connection between optical measurements concerning disorder and charge transport in transistors.

View Article: PubMed Central - PubMed

Affiliation: Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, United Kingdom.

No MeSH data available.


Related in: MedlinePlus