All-Solution-Processed OLEDs Using Printed Ag Electrodes and a PEI Bonding Layer

Abstract

We demonstrated a bonding technology using polyethyleneimine (PEI) as a bonding layer between printed Ag electrodes and an emission material layer (EML) to fabricate all-solution-processed Organic LightEmitting Diodes (OLEDs). We manufactured Ag electrodes on a glass substrate by the screen printing method, which was bonded to another substrate with ITO anodes and an EML layer using a PEI layer. Since the bonding layer needs to have both good bonding characteristics and electrical conductivity, we investigated how both characteristics were affected by some experimental factors, namely, PEI concentration, the thickness of the layer and additives. The bonding strength and the electrical current density were investigated by tensile tests and electron only device (EOD) experiments, respectively. The results showed that at higher PEI concentration the bonding strength reached a higher value, but the electrical current through the PEI layer decreased rapidly with increased PEI layer thickness. When sorbitol was added into the PEI solution, both bonding strength and electrical conductivity were improved, and when 10 wt% of sorbitol was added into 0.1 wt% PEI solution, the device showed an electrical current density of 1,000 mA/cm<sup>2</sup> and a good bonding strength also. Finally, we manufactured a two-substrate OLED device using the bonding layer and measured the luminance, which revealed that the device turned on at 4 V and the maximum luminance was 7,000 cd/m<sup>2</sup>. These data, both electrical and optical, demonstrate the potential to fabricate all-solution-processed OLEDs using the two-substrate bonding technology.