Inkjet-printed multilayer structure for low-cost and efficient OLEDs

Inkjet printing is considered a key technology in the fabrication of organic light-emitting diodes (OLEDs), but achieving a fully inkjet-printable OLED structure is still a challenge. Here, we propose the fabrication of OLEDs with an inkjet-printed multilayer structure (i.e. anode/hole injection layer (HIL)/electron blocking layer (EBL)/ emitting layer (EML)) by properly developing new HIL and EBL inks to achieve uniform and homogeneous printed thin films. In the fabricated multilayer device, the dissolution process of the EBL, which occurs during the printing of the EML, creates a blurred interface, resulting in device performance that achieves maximum current efficiencies of 20 cd/A and 7 cd/A with ITO and printed polymeric anode, respectively. With the aim of simplifying the structure of the device and mimicking the formation of such a blurred interface, another printed multilayer structure (i.e. anode/printed HIL/printed EBL:EML) was proposed, achieving maximum current efficiencies of 13 and 6 cd/A with ITO and polymeric anode, respectively. Such results represent a compromise between simplifying the fabrication process and achieving good electro-optical properties and thus represent a further step towards the fabrication of a fully inkjet-printed ITO-free OLED.