Dear Ershad,

Welcom,

Adding to the above ,which is seen is not waves t is nonhomogeneous thickness of the deposited film. Also, one can see dust particles or deposits of particles formed in your solution.In addition the underlying surface of the substrate is not very clean. I have the impression that it contains stains.

So, to get a homogeneous thickness of the deposits you should:

-Clean the substrate to become free of any contamination

- prepare the solution such that it is homogeneous with no particle formations. 

-The solution must have the proper viscosity to spread homogeneously during spin on

- You have to adjust the speed of the spinning. and the spinning time.

- consult the literature on spin process of pervoskite  thoroughly.

wish you success

Hi dear Ershad

These wave forms you see appear in spin coating and any wet procedure film deposition due to attraction repulsion between polarised molecules in the solurion i.e. water molecules. Especialy on water reppelant underlayers like Si (If I have chosen the right word ). I devised a procedure to overcome this irregularities,  by conducting deposition in saturated vapor of precursor.  I devised my chamber by using a glass box and a pressure meter, and I think probably there is an actual devise for such reason maybe where you do your research.  I hope it helps you.

Dear Laleh

Many thanks for your response. I thought, these waves occur because of the under-layer undispersed TiO2 particles which obstacles the movement of perovskite precursor solution during spin coating system. what's your opinion about this idea? If you look carefully, you can see little particles on the waves.

I didn't work with TiO2 so my response may be not so accurate.  But check  if your sol/gel is stable and these particle are not precipitation. Especially if any heat is associated with your procedure which may result in local precipitation. But if you have any doubts about the possible TiO2 contamination you can use Edx or any composition test to become sure. 

Thanks for your helpful comment. I will do the test. 

Dear Ershad,

Welcom,

Adding to the above ,which is seen is not waves t is nonhomogeneous thickness of the deposited film. Also, one can see dust particles or deposits of particles formed in your solution.In addition the underlying surface of the substrate is not very clean. I have the impression that it contains stains.

So, to get a homogeneous thickness of the deposits you should:

-Clean the substrate to become free of any contamination

- prepare the solution such that it is homogeneous with no particle formations. 

-The solution must have the proper viscosity to spread homogeneously during spin on

- You have to adjust the speed of the spinning. and the spinning time.

- consult the literature on spin process of pervoskite  thoroughly.

wish you success

You should consider the precursor solution dissolution, try to  filter solutions before spin-coating. clean the surface of TiO2 before perovskite deposition.  

Dear Prof Zekry

As you told, I can see the contaminations on my tio2 layer ... I am pretty sure the FTO substrate is clean ... cause we use Ultrasonic bath in 4 levels, heat-treatment at 500 for about 30 minutes and UV-Ozone for about 15 minutes. The  TiO2 solution viscosity parameter is serious ... Would you please suggest me a proper viscosity testing method for this issue?

Dear Ludmila

thanks  for your cmnt ... we filter our solutions with 450 nm and 220 nm filters ... do you clean the surface with air blower? or do you have other suggestion to clean the surface before perovskite deposition? for example UV-Ozone after TiO2 deposition? 

Dear Ershad,

How are you.

I hope you solved your problem. It will be good if you notify us about your experience.

As for the TiO2 you can filter out the suspension to decrease the aggregation of of its particles and reduce the formation of the non homogeneous film layer.

Best wishes

I encountered such a problem with my films as well. Are you preparing the films in the open environment? or inside the glove box. if you are not using glove box, then it must be the reason to it. Otherwise, increase the spinning speed and throw the solution on the already spinning substrate and leave the film for sometime to rest on the spinner before thermal annealing.