I am trying to get grains of perovskite for which I am using hot casting method. I made solution of methyl ammonium iodide and lead iodide in DMF. I am sometime getting wires like structure and sometime grain like structure. I am doing this in glovebox and spin coating at 2500 rpm for 15 s. The substrate is heated at 170 degree Celsius and and solution at 60 degree Celsius.
The formation of grains by deposition of supersaturated solutions depends on the seed formation phase and the following subsequent grains growth phase. This prosses depends on the substrate material, temperature and the the rate of deposition. The grains will be greater when the numbers of seeds becomes smaller.
In order to measure the grain size one can use a microscope with sufficient resolution such as the electron microscope. There is the scattering electron microscopy and transmission electron microscopy. The scattering electron microscopy is suitable for measuring the grain size. You van use optical microscope also with the required resolution.
Best wishes
Further Abdelhalim's suggestions, the controlling a solution process to fabricate a film with certain grain sizes is a complicated task. Even more difficult to do inside the glovebox due to the purging inert gas either nitrogen or argon. Your spincoating duration is so short that a solution on the coated substrate may not be completely dried. This could cause the problem to control your film condition. I would suggest the spincoating duration is longer than 15s. Normally we use 60s to get dried films. What i meant is that after spincoating, you should not see any solvent evaporating from the surface of the films. Another issue could occur as well after fininsh spincoated one sample to make second one. Some solvent may be left over inside the spincoater. This can influence on your next sample. Once you control the above process, you should be able to have consistant results. Hope it helps.
Thank you Xuhua Wang and Abdelhalim abdelnaby Zekry for your suggestions
Hi Xuhua Wang I tried to drop cast precursor solution (PbI2+MAI in DMF maintained at 70 degree) on a hot glass substrate maintained at 180 degrees. I waited for 15 s and then spin coat it at 2520 rpm for 15 s. After doing so, I immediately transfer it to hot plate maintained at 180 degree and wait for 5 s to get brown colored film of perovskite. On this film when I checked through optical microscope, I sometimes get wire like structure and sometimes grain like structure. But if I place it on hot plate for more than 5 s, it agaian changes back to yellow colored film. How can I be consistent with it?
Dear Bibek,
I would suggest that you do a systematic study with the perovskite films in order to control the process with different temperatures. In this way you can find out what it is going on with the phase changing of your films under a certain condition. Then you can control your process. At the meantime, your results will be valuable for your work to be published. Alternatively you can also study your materials or films phase changing using DSC. Hope it helps.
I guess the problem is that you did not get a good solution before spin coating. I suggest to use GBL as the solvent instead of DMF.
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