The stability of the interface between indium-tin-oxide (ITO) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) in polymer light-emitting diodes (p-LEDs) was investigated. The study found that the ITO/PEDOT:PSS interface is not stable, leading to degradation of the device performance. In as-prepared samples, 0.02 at. % indium was detected in the PEDOT:PSS film due to etching of the ITO during spin coating. Annealing in a nitrogen atmosphere at 100 °C for 2500 hours increased the indium concentration to 0.2 at. %. However, exposure to air caused a much faster degradation, with the indium concentration reaching a saturation of 1.2 at. % after several days. This degradation is attributed to the strong acidic nature of PEDOT:PSS, which etches the ITO. The study also found that the indium-containing etch products are trapped in the PEDOT:PSS layer, preventing their diffusion into the overlying polymer layer.The stability of the interface between indium-tin-oxide (ITO) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) in polymer light-emitting diodes (p-LEDs) was investigated. The study found that the ITO/PEDOT:PSS interface is not stable, leading to degradation of the device performance. In as-prepared samples, 0.02 at. % indium was detected in the PEDOT:PSS film due to etching of the ITO during spin coating. Annealing in a nitrogen atmosphere at 100 °C for 2500 hours increased the indium concentration to 0.2 at. %. However, exposure to air caused a much faster degradation, with the indium concentration reaching a saturation of 1.2 at. % after several days. This degradation is attributed to the strong acidic nature of PEDOT:PSS, which etches the ITO. The study also found that the indium-containing etch products are trapped in the PEDOT:PSS layer, preventing their diffusion into the overlying polymer layer.