Water-Processable Self-Doped Hole-Injection Layer for Large-Area, Air-Processed, Slot-Die-Coated Flexible Organic Light-Emitting Diodes

• Published in: Chemistry of materials Vol. 35; no. 21; pp. 9102 - 9110
• Main Authors: Gasonoo, Akpeko, Beaumont, Catherine, Hoff, Anderson, Xu, Chaochen, Egberts, Philip, Pahlevani, Majid, Leclerc, Mario, Welch, Gregory C.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.11.2023
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.3c01784

Hole-injection layers (HILs) play a pivotal role in organic light-emitting diodes (OLEDs) by enabling the efficient injection of positive charge carriers (holes) into the active layer, thus facilitating light emission. This research paper focuses on enhancing the processability and performance of solution-processed HILs in OLEDs by utilizing a water-processable self-doped polymer, P2. The P2 film, deposited via slot-die coating, exhibits exceptional uniformity, high transmittance (85%) across the visible spectrum, and a smooth surface (with a root-mean-square roughness of 1.4 nm) comparable to state-of-the-art poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) films. The P2 HIL in a four-layer OLED structure, consisting of a PET/ITO/HIL/hole transport layer (HTL)/emissive layer (EML)/electron transport layer (ETL)/Ag, with poly­(9-vinylcarbazole) (PVK) as the HTL, Super Yellow (SY) as the EML, and poly­((9,9-bis­(3′-(N,N-dimethylamino)­propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) (PFN) as the ETL, demonstrates enhanced hole injection and transport properties. Flexible OLEDs incorporating P2 HILs, fabricated and tested under ambient conditions on a large-area (4 × 40 mm) indium–tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate, demonstrate a maximum current efficiency of 1.24 cd/A, surpassing devices with PEDOT:PSS HILs by 82%. Moreover, a significant 50% reduction in turn-on voltage is observed compared with analogous devices using a PEDOT:PSS layer. This work contributes to the advancement of the OLED technology for various commercial optoelectronic applications.