• Work in Class 100 conditions
• Clean all substrates in an ultrasonic bath with warm 5% Decon 90 or similar phosphate-free reagent
• Filter all liquids to 0.02 microns or better
• Ensure substrate is wetted fully by the liquid. Ethanol should be fine

Dear Amirhossein,

me seems the wetting of the substrate by the liquid is the problem. You must differ between hydrophil and hydrophob surfaces. The surface properties - purity, roughness and contaminations (greaseless) influence the behaviour.

With regard

R. Mitdank

@amirto remove pin holes I'll list down the most important to less important parameters for your reference which affects the pin hole

1. Substrate and thin film nature( like attracts like, hydrophilic suface like hydrophilic films and vice versa) it's mostly true but in some cases it's opposite. So you may play with substrates. Or you may treat substrates accordingly silanes/plasma etc.

2. Dust particle heavily affect the pin holes. Get rid of it. By cleaning the substrate, clean lab, filter etc

3. Optimization of speed and time of rotation.

4. Suspended particles in solution. If you have any suspended particles try filtering it with syringe filters. Also, make sure while you filter, bubbles don't come upon your film.

5. Wander wall forces, let your solution to be there on substrate for some time. It leads to better adhesion

6. Partial pressure also plays a role

7. Humidity also plays a role

8. Baking temperature also plays the role. You make bake at low temperature and then move to high temperature. In some cases it gives good uniformity.

9. Rotary Chuck wobbling nature gives non uniform film

10. Avoid warping of substrate (for flexible substrates)

I think you have to optimize two parameters viz. nature of substrate and methodologies used for coating.

Some time heating the sample may improve the quality of your film.

- Heating the substrate at a temperature similar to the ink temperature to avoid thermal chocs.

- Doing the spin coating operation in a closed 'spin-coater' and saturated with the used solvent