Abstract
Currently, the low yield, high power loss, and poor stability of organic light emitting diodes (OLEDs) panels are
remaining as the obstacles to the fast growth of the OLED industry, especially for the lighting application. The p-i-n
OLEDs have been widely recognized as the promising method to circumvent these bottleneck factors, due to the unique
merit of the electrical doping to enable low power loss. In p-i-n OLEDs, the frequently used n-doped electron transport
layers (n-ETL1) such as n-BCP, n-Alq3 possess markedly lower conductivities but better capabilities of injecting
electrons into ETL such as BCP, Alq3, as compared to another class of n-doped ETLs (n-ETL2), e.g., n-NTCDA, n-PTCDA, n-C60. Thus, in order to minimize the electron loss, we provide the structure of uniting two n-doped layers,
cathode/ n-ETL2/ n-ETL1/ ETL. In p-i-n OLEDs, the hole current injected from the single p-doped hole transport layer (p-HTL) into the neat HTL must be limited, because the higher conductivity p-HTL has the higher lying highest
occupied molecular orbital (HOMO) level, leading to a larger hole transport energy barrier (φB) at the interface with the
neat HTL. Therefore, in order to minimize the hole loss, we suggest the structure of uniting two p-HTLs, anode/ p-HTL2/
p-HTL1/ HTL. The p-HTL2 possesses high-lying HOMO level and thereby high conductivity, decreasing the ohmic loss in the hole conduction; the p-HTL1 features a low-lying HOMO level, reducing the φB.
