Extremely low-voltage driving of organic light-emitting diodes with a Cs-doped phenyldipyrenylphosphine oxide layer as an electron-injection layer

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Abstract
We demonstrated efficient electron injection and transport in organic light-emitting diodes using an electron-transport layer (ETL) composed of a Cs and phenyldipyrenylphosphine oxide ( P O Py 2 ) co-deposited layer. In particular, an ETL composed of a Cs : P O Py 2 layer with an atom:molar ratio of 1:2 demonstrated an extremely low driving voltage, resulting in a high current density of 100 mA ∕ cm 2 at an applied voltage of only 3.9 V. The results of Kelvin probe and absorption measurements indicated that the formation of a CsAl alloy layer at the Cs : P O Py 2 /Al cathode interface and the charge-transfer complex between the Cs and P O Py 2 contributed to enhancing the efficiency of electron injection and transport, respectively.