Every where in the texts, papers, etc.. people talk about what should we do to replace this high-cost hole transport material (Spiro-OMeTAD), but there is nothing about the main reason(reasons) which made it the most efficient HTM. I will be gratefull to know how it get started? because high mobility? high conductivity? low recombination rate? or..?
Dear Saeede
There are certain properties which makes a material good HTM. Majority of HTMs reported in literature lacks few or more properties. These properties include high glass transition, smooth film morphology, electrochemical stability, optical transparency (should not absorb in visible region), amorphous nature etc. If you try to deliberately go through the various properties of all reported HTMs, then you will find that only few materials actually satisfy all the conditions. More the conditions it satisfy, more efficient it will be. For more detail you can read my paper.
Though material with higher hole mobility should be considered better HTM but sometimes (In OLEDs) slower hole mobility is desired to balance charge recombination as holes travel faster that electrons in organic materials.
Dear Gopal
Thanks for your useful information about what properties make HTM efficient. I was wondering, whether Spiro-OmeTAD has all of these advantages or not?
If a material is being used as HTM, it doesn't necessarily mean that it possess all the properties. It can be more advantageous than other materials being used. You will have to manually look into all properties and then compare it with other materials. Only then you will find the actual reason of its use and will also come to know what type of more improvements are required in it to design a better material.
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