Enhanced performance of blue OLED with water/alcohol soluble conjugated polymer as electron injection layer

Abstract

In this work, a water/alcohol-soluble conjugated polymer poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9–dihexylfluorene)] (PFNC6) is synthesized and the photophysical properties are investigated. Subsequently, it is tested as electron injection layer in a blue emitting OLED with PFO. The maximum current efficiency (CE) and external quantum efficiency (EQE) of the device increased by 3 times to 0.75 cd/A and 0.66%. Further enhancement in the OLED performance is obtained when a bilayer electron injection consisting of PFNC6 and LiF are used where the maximum CE is 2.16 cd/A and the maximum EQE is 1.55%. Measurement with electron-only-devices confirmed that the electron mobility is increased for the device with PFNC6 as compared to the control device. Furthermore, higher Vbi is obtained in photovoltaic measurement when PFNC6 is used. As a result, the electron injection barrier is reduced and electron injection is more efficient.