It seem to observed slightly injection of the electron at low Vg. How much is the Vds of the curves. Try to measure the transfer characteristic under lower Vds if you want to obtain the off state of the transistor.

Hello,

Check if the gate current is low at threshold. If it is not, I suggest to scratch the semiconductor all around the S & D électrodes to avoid leakage current (with the probe of your I(V) setup). Also, remove the semiconductor at the edge of the substrate to  prevent electrical contact between the semiconductor and the gate.

Hi,

1. Use 50-60 nm thick electrodes, (optional:try bottom contact bottom gate or bottom contact top gate).

2. Use 3-5 mg/ml TIPS-pen solution.

3. If you want to grow ribbon like crystals, you dont need to incline. Keep things simple, it will work. Vary the drying rate by placing substrate on hot plate.

4. Try filtering just solvent before using.

5. Make sure, you are cleaning substrates well. (Acetone, IPA, Ethanol, RCA-1, UV ozone)

6. I dont think your transfer curves are bad. This is mainly due to inhomegeneous drop cast film. If you look under the microscope, you will see, good performance is coming from highly aligned and comparetively homogeneous film section.

Thank You Jian, Olivier and Muhammad for your valuable inputs.

Vds of the transfer curve is -50 V.

I have already seen by scratching the semiconductor around S/D electrodes, but no change in transfer characteristics. Removal of the semiconductor from the edges of the substrate is a good idea, which I will definitely try.

Can I obtain small and homogeneous  crystals using 3-5 mg/ml TIPS solution?

Because, the issue of homogeneous nature of crystals seems true, Because I have also observed similarly that good characteristics curves are obtained mainly from small, aligned  and homogeneous crystals of lesser height.

Is there any way to get these small crystals on entire substrate?

For ex. if I  don't incline and use 3-5 mg/ml TIPS solution, are there chances for improvement in the off state?

Also, If I want to use a polymer with TIPS (for blend OTFTs) in 1:3 ratio, is 3-5 mg/ml conc. sufficient?

current values in bad characteristics curves are > 100 nA at 0 volts, which are not usual in the first sight.

If you drop cast, you wont be able to get uniform films. 

Spin coating will give you homegeneous films but at the cost small crystals with mixed phases(face on & edge on). 

Knife coating/ blade coating or slot die coating will give you best results for this material. These coating techniques offer easy and scalable way to coat highly alligned crystals.

Removing excess material will not affect transfer curves. It mainly reduces leakage currents and may improve output curves.

Thank You for response.

If I want to use a polymer with TIPS (for blend OTFTs) in knife/blade coating in 1:3 ratio, is 3-5 mg/ml conc. of TIPS Pentacene sufficient?

Yes, its enough.

I was going through one of your report on blends, where semiconductor and polymer were used with similar conc. (~ 1 wt%). If I am lowering the semiconductor conc., then do I need to lower  the polymer conc. also?

Thanks for your valuable suggestions...I hope this will help greatly...