The negative effect of toluene on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole injection layer and its role in reducing the stability of solution-coated organic light-emitting devices

Abstract

The effect of toluene, a solvent commonly used in fabricating hole transport layers (HTLs), on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole injection layer and its role in reducing the stability of solution-coated organic light-emitting devices (OLEDs) is investigated. In order to isolate and study the effect of solvents on the hole injection layers alone, only the PEDOT:PSS is exposed to the toluene, whereas the other device layers are fabricated by vacuum-deposition. Results show that the solvent exposure leads to a significant decrease in device electroluminescence (EL) stability, revealing that the phenomenon plays a role in the lower stability of devices with solution-coated HTLs. The solvent exposure is found to reduce hole injection efficiency, possibly due to changes at the PEDOT:PSS/HTL interface, a phenomenon that likely plays a role in the lower EL stability. The findings bring to light one of the major root causes of the lower stability of solution-coated OLEDs.