Currently, I am studying the working on the OLED screens in detail. I have come across various layers of systems, for example, HIL, HTL, ETL, EIL and EML. I have studied that each layer has energy difference in it. Why that is? is it necessary? why can't we directly connect the Emissive layer to the Anode and Cathode? what is the role of the energy barrier in it? I am adding one image with this question.
Dear Prerna,
Indeed one of the first OLEDs was an anthracene crystal connected to an anode and cathode. However, these simple OLEDs were not very efficient, due to the low EL and light extraction efficiency. Therefore, muiltilayer OLEDs were invented to improve the efficiency of radiative recombination of charge carriers. This also implies the use of aligned electronic states to foster the charge carrier flow. Appended you will find a chapter of my lecture, which might help a bit.
All the best,
Thomas
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