Single-Step PEDOT Deposition by oCVD for ITO-Free Deep Blue OLEDs

International audienceOrganic light-emitting diodes (OLEDs) are emerging technologies for potential lighting and display applications. Transparent conductive electrodes (TCEs) play a crucial role in enabling the functionality and increased performance of these particular devices. Despite their widespread use, indium tin oxide (ITO) thin films have several significant drawbacks, including material scarcity, high costs associated with both materials and fabrication processes, and limited flexibility. To address these issues, we thoroughly investigate the deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films as a promising alternative to ITO using a single-step and dry method named oxidative chemical vapor deposition (oCVD). The impact of increasing the substrate temperature from 110 to 190 °C on the film’s structure and properties was revealed with an increase in the film conductivity to over 1600 S/cm at 170 °C and a total transmittance of 97% in the visible range. This increase was attributed to a change in the molecular structure of the conjugated polymer from benzoid to quinoid as revealed by Raman and FTIR measurements. The XPS results demonstrated an increase in the doping ratio with Cl-containing species and a reduction of impurities. GIXRD, HR-TEM, and AFM measurements indicated a smooth surface and a highly face-on orientation for all temperatures. The optimized TCE layers were successfully integrated into deep blue OLED devices emitting at 436 nm with stable color Commission Internationale de l’Energie (CIE) coordinates of (0.15, 0.08) under variation of the applied current. A satisfactory performance (72.1 cd/m2 and 0.86 W/sr·m2 at 10 mA cm–2) and an external quantum efficiency (EQE) of 1.04% were achieved. These results are quite promising, as OLEDs based on PEDOT as a TCE have demonstrated slightly better output performance in terms of luminance and radiance, with an increase in EQE by a factor of 1.7, compared to the reference device based on ITO