Fabrication of Transparent CNT Films for OLED Application

We optimized the process to prepare SWCNT solutions with the good degree of dispersion of individually isolated SWCNTs. The thin-film casting by spin-coating resulted in SWCNT films with uniform sheet resistance and visible-light transmittance. With the control of the spin-coating conditions we were able to control the thickness, sheet resistance and visible-light transmittance with the general trend that the reduction of sheet resistance requires the sacrifice of visible transmittance. Further reduction of the sheet resistance with a limited sacrifice of visible-light transmittance was achieved through the treatment of SWCNT films with nitric-acid. Another process that we developed for more efficient reduction of the sheet resistance was the combination treatment of SWCNT films with HNO3 and SOCl2. This new process turned out to be more stable against undesired increase of the sheet resistance due to the inevitable heating that the SWCNT would experience during the OLED fabrication. It appears that the doping and de-doping effects are more prominent in the combination treatment with HNO3 and SOCl2, as evidenced by the suppression and recovery of the van Hove singularities in response to the combination treatment and heating. More evidence for the anodic doping electron withdrawal due to the combination treatment was found from the resonance Raman scattering. The distinct Raman modes of the some semiconducting SWCNTs that appeared strong because of the resonance of the excitation energy 1.15 eV with the S22 transition became substantially weak after the HNO3-SOCl2 combination treatment. One of the key process steps for OLED fabrication on SWCNT electrodes is the anode patterning.