As I understood, one of the reasons of high series resistivity in solar cell devices is non-complete oxidation of spiro-OMeTAD. Which conditions (humidity, temperature, duration, oxygen or air environment, dark or light?) are required for full oxidation of 200-300 nm of it? Thank you ahead!
You can also carry out chemical oxidation of spiro using some oxidant, like NOBF4, Ag salts, Co-complexes etc. But it really depends what do you wanna use it for.
Similar to Matthew's answer, we also found that leaving the doped layer (LiTFSI, TBP additives) in a dry air desiccator overnight in the dark is sufficient for proper oxygen doping (although 300 nm sounds a bit too thick).
However, we also found that different sources of spiro requires different amount of additives to reach similar performance. We still do not know why this is so, but suspect the water content in the material is the source.
Thank you all for your detail answers.
I am totally agree with Dr. Saar about different sources of spiro. In some cases using of low concentration of LiTFSI is OK, but in other cases - only its high concentrations results in better performances. Which concentration did you find to be optimal for perovskite devices? Do you usually clean spiro before using (sublimation, vacuum...)? And also which parameters of spin coating (2000 or 4000 rpm?, 1000-4000 rpm/s? 30-60s?) do you think are suitable for spiro deposition? As we found, acceleration is more important rather than spin speed. 2000 rpm/s gives full-covered layer, but thick. 4000 rpm/s gives thinner, but too many scratches.
Thank you in advance!
Matthew,
Why must the spiro be in the dark? Wouldn't light help to oxidize the spiro? Also does it work faster if you put your samples in a chamber filled with pure oxygen?
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