Role of K2CO3 as an n-type dopant in enhancing the electron injection and transport of organic light-emitting devices

Potassium carbonate (K2CO3) has demonstrated to be an efficient n-type dopant in improving the performance of the Alq3-based organic light-emitting diodes (OLEDs). K2CO3-doped tris(8-hydroxyquinolinato)aluminum (Alq3) layers with various concentrations were prepared by the co-evaporating method and the role of K2CO3 was investigated. When 10% K2CO3 was doped into an Alq3 electron-transporting layer, device properties such as the turn-on voltage, the maximum luminance, and the device efficiency were improved. K2CO3-doped Alq3 layers possess an enhanced electron injection and transporting ability. The higher mobility of the K2CO3-doped samples has been derived using space–charge–limited current (SCLC) measurements. X-ray and ultraviolet photoelectron spectroscopy results show that some electrons transfer from K2CO3 into Alq3, which increases the electron concentration in Alq3 films and moves the Fermi level close to the lowest unoccupied molecular orbital (LUMO) of Alq3. Therefore, the electron injection and transport efficiency are both enhanced due to a lower electron injection barrier and a higher electron mobility, which improve the charge carrier balance in OLEDs and lead to better device efficiency.