Hi;

I previously coated FTO with BiFeO3 by spin coating. I think you need a slower initial rotation speed to get a continuity. As far as I remember, I set the initial speed to 500 rpm and then increase the rotation as needed thickness.

Wish to success.

Regards.

First off, you should try to enhance the wettability of the substrates by plasma treatment. You may find that even a simple corona discharge treatment by a low cost piece of equipment will result in significant improvements. You can try lower spinning speeds, multiple coating cycles (either drop by drop during spinning, or intermittent repetitions) or increasing the viscosity of the sol (by changing composition or concentration). Using acetate precursors may yield a thicker sol, more amenable for spin coating thicker layers.

The rotation speed (rpm) must be adjusted because increasing it will make the coating concave due to the central force.Take the appropriate surface temperature,This helps in coating adhesion.