Influence of PVK Hole Transport Layer on Ndq3Near-infrared Organic Light Emitting Diodes

A three-layered near-infrared OLED with structure of ITO/PEDOT∶PSS/PVK/neodymium tris-(8-hydroxyquinoline)(Ndq3)/Al was fabricated,in which poly(N-vinylcarbazole)(PVK) was hole transport layer,and poly(3,4-ethylene dioxythiophene)∶poly(styrenesulfonate)(PEDOT∶PSS) was hole injection layer.The EL spectrum shows three emission peaks at 905,1 064,1 340 nm in the near-infrared range which are correspond to Nd3+ transitions of 4F3/2→4I9/2,4F3/2→4I11/2,4F3/2→4I13/2,respectively.The influence mechanism of functional layers was discussed with help of I-V curves,in reference with single layer device(ITO/Ndq3/Al) and double layer device(ITO/PVK/Ndq3/Al).The increase in device current corresponding to the reduction of the series resistance was observed and was related to the high conductivity of PEDOT∶PSS layer.The joint action on the hole injection barrier by PVK and PEDOT∶PSS was contributed to the improvement of the charge carriers balance of device and EL emission intensity.Also,the decrease of the ITO surface roughness was realized as one of the key issue for the performance improvement.