Organic thin film transistor with dual layer electrodes

1. A thin-film transistor, comprising:

a source electrode; a drain electrode; a gate dielectric layer; and

a polythiophene semiconductor layer;

wherein the source electrode and drain electrode each comprise a first layer and a second layer, the first layer directly contacting the dielectric layer and separating the second layer from the dielectric layer, the second layer directly contacting the semiconductor layer;

wherein the source electrode first layer has a work function differing from the energy level of the semiconductor layer by at least 1.0 eV;

wherein the source electrode second layer has a work function differing from the energy level of the semiconductor layer by at most 0.2 eV;

wherein the semiconductor layer has a channel length of from about 1 to about 5 micrometers; and

wherein the transistor has a mobility of at least 0.39 cm 2 /v·sec and a current on/off ratio of at least about 10 7 .

2. The thin-film transistor of claim 1 , wherein the source electrode first layer, the drain electrode first layer, the source electrode second layer, and the drain electrode second layer independently comprise a material selected from the group consisting of titanium, platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony, lead, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin oxide-antimony, indium tin oxide, fluorine-doped zinc oxide, zinc, carbon, graphite, silver paste, carbon paste, lithium, beryllium, sodium, magnesium, potassium, calcium, scandium, manganese, zirconium, gallium, niobium, sodium, sodium-potassium alloy, magnesium, lithium, and alloys thereof.

3. The thin-film transistor of claim 1 , wherein the source electrode first layer and the drain electrode first layer each have a thickness of at most 50 nanometers.

4. The thin-film transistor of claim 1 , wherein the source electrode first layer and the drain electrode first layer each have a thickness of from about 5 nanometers to about 50 nanometers.

5. The thin-film transistor of claim 1 , wherein the source electrode second layer and the drain electrode second layer each have a thickness of at least 5 nanometers.

6. The thin-film transistor of claim 1 , wherein the source electrode second layer and the drain electrode second layer each have a thickness of from about 20 to about 1000 nanometers.

7. The thin-film transistor of claim 1 , wherein the semiconductor is a p-type semiconductor.

8. The thin-film transistor of claim 1 , wherein the source electrode first layer, the drain electrode first layer, the source electrode second layer, and the drain electrode second layer each directly contact the semiconductor layer.

9. The thin-film transistor of claim 1 , wherein the source electrode second layer has a work function matching the energy level of the semiconductor layer.

10. An organic thin-film transistor, comprising:

a source electrode; a drain electrode; a gate dielectric layer; and

organic polythiophene semiconductor layer;

wherein the source electrode and drain electrode each comprise a first layer and a second layer, the first layer directly contacting the dielectric layer and separating the second layer from the dielectric layer;

wherein each first layer has a work function differing from the energy level of the semiconductor layer by at least 0.5 eV;

wherein each second layer has a work function differing from the energy level of the semiconductor layer by at most 0.2 eV; and

wherein the semiconductor layer has a channel length of from about 5 to about 10 micrometers; and

wherein the transistor has a mobility of at least 0.39 cm 2 /V·sec and a current on/off ratio of at least about 10 7 .

11. The thin-film transistor of claim 10 , wherein the difference in work function between the semiconductor layer and each first layer is from 0.5 eV to about 1.0 eV.

12. The thin-film transistor of claim 10 , wherein the difference in work function between the organic semiconductor layer and each first layer is at least 1.0 eV.

13. The thin-film transistor of claim 10 , wherein the source electrode first layer and the drain electrode first layer each comprise titanium.

14. The thin-film transistor of claim 10 , wherein the source electrode second layer and the drain electrode second layer each comprise gold.

15. The thin-film transistor of claim 10 , wherein the transistor is a bottom-gate bottom-contact transistor.

16. A bottom-gate bottom-contact organic thin-film transistor, comprising:

a dielectric layer;

a source electrode; a drain electrode; and

a polythiophene semiconductor layer;

wherein the source electrode and drain electrode each comprise a first layer of titanium and a second layer of gold, the first layer directly contacting the dielectric layer and separating the second layer from the dielectric layer, the second layer directly contacting the semiconductor layer; and

wherein the semiconductor layer has a channel length of at most about 10 micrometers;

wherein the transistor has a mobility of at least 0.39 cm 2 /V·sec and a current on/off ratio of at least about 10 7 .