*1.2.4 Charge transport phenomena*

The PI films can be amorphous or crystalline, depending on their synthesis chemistry. In these regions, the trap energy of electrons varies according to the band structure [11]. The high electric field stresses create more trap levels in the insulation, especially at the top and bottom surface of samples near to the electrodes. These trap levels reduce toward the interior regions. In **Figure 2**, a thin PI film is placed between two electrodes. The layer near to anode can act as hole transport layer, and the layer near to cathode can act as electron transport layer. The intersection region of these layers can provide enough space for the recombination of electrons and holes that are injected by electron

### **Figure 2.**

*PI film layer structure, hole injection layer (HIL), hole transport layer (HTL), electron transport layer (ETL), electron injection layer (EIL).*
