Organic light emitting diodes fabricated with single wall carbon nanotubesdispersed in a hole conducting buffer: the role of carbon nanotubes in a hole conducting polymer

In order to investigate the role of single wall carbon nanotubes (SWNTs) in a hole conducting polymer, organic light emitting diodes (OLEDs) were fabr icated with a conjugated emissive copolymer, poly(3,6-N-2-ethylhexyl carbaz olyl cyanoterephthalidence) (PECCP) and SWNTs dispersed in a hole conductin g buffer polymer, polyethylene dioxythiophene (PEDOT). Devices made with SW NTs dispersed in PEDOT and devices made without SWNTs in the PEDOT emit gre en light at 2.37 eV as expected for PECCP. However, we observed that the de vice made with SWNTs in the buffer layer shows a significant decrease in th e electroluminescence (EL) as compared to that of the device without the SW NTs, In contrast, the photoluminescence (PL) from the same organic layer co mbination, excited from the PECCP side and measured through the PEDOT and t he indium tin oxide glass, shows very little difference between the films w ith and without the SWNTs. The current-voltage (I-V characteristics of OLED s with SWNTs show a lower I-V power dependence (I-V-2) near 1-2 V than that of the device without SWNTs which has a power dependence of I-V-5. The EL and the E-V data together with the PL suggest an electronic interaction bet ween the SWNTs and the host polymeric material, PEDOT. We propose that this electronic interaction originates from the hole trapping nature of SWNTs i n a hole conducting polymer. (C) 2001 Elsevier Science B,V, All rights rese rved.