Dear Boukhili,

The cathode material builds with the organic active material a metal semiconductor contact which can behave either ohmic or rectifying Schottky contact. In case of ohmic contact the barrier between the Metal and the organic semicondcutor ie either low or tunnel able such that it allows easily the passage of carriers across it. In this case the current will be controlled by the charge transport in the organic materials.

When there is an appreciable barrier it will impede and control the injection of the mobile carrier across it.

I treated this point in a RG link: https://www.researchgate.net/post/How_is_the_current_limited_in_metal_organic_semiconductor_metal_MOSM_diode

Best wishes

Dear Boukhili,

The cathode material builds with the organic active material a metal semiconductor contact which can behave either ohmic or rectifying Schottky contact. In case of ohmic contact the barrier between the Metal and the organic semicondcutor ie either low or tunnel able such that it allows easily the passage of carriers across it. In this case the current will be controlled by the charge transport in the organic materials.

When there is an appreciable barrier it will impede and control the injection of the mobile carrier across it.

I treated this point in a RG link: https://www.researchgate.net/post/How_is_the_current_limited_in_metal_organic_semiconductor_metal_MOSM_diode

Best wishes

Thanks Dr Abdelhalim Zekry

Further Abdelhalim's comments, an OLED design requests both electron injection and hole injection on cathode and anode sides. Majority of organic semiconductors have higher hole mobilities than their electron mobilities. The energy alignments between the work function of a cathode and the LUMO of electron injection of organic semiconductors are critical. This very often leads to lower workfuction metal cathode such as Ca or Ba used within an OLED device. Although there are some other types of materials used to improve the electron injection such as LiF and metal oxides, the mechanism is slightly different from the low work function cathode. There are many references you could find. Please be aware of that Organic semiconductors are very different from inorganic semiconductors in term of energy levels and charge carrier mobility.

Hope it helps.