Optimizing OLED performance on polyimide substrates: Evaluation of ITO and organic layer thicknesses with different encapsulation materials

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We investigate the electro‐optical properties of indium tin oxide (ITO) transparent electrodes on polyimide (PI) and glass substrates and their impact on organic light‐emitting diode (OLED) performance. At a given thickness, the ITO layer exhibits a lower sheet resistance on glass substrates compared to PI substrates. The optical transmission spectra of ITO films are also analyzed, revealing substantial variations owing to interference phenomena. The optimal ITO layer and electron transporting layer (ETL) thicknesses for maximizing the luminance are identified, with glass substrates achieving higher luminance. The luminance on PI substrates shows smaller changes owing to their refractive indices being similar to those of the organic layers. Device fabrication confirms the simulation results, showing that luminance on PI substrates is more sensitive to ETL thickness. Incorporating SiN x and Al 2 O 3 as thin‐film encapsulation shifts the optimal ITO layer thickness and slightly reduces luminance. Replacing SiN x with SiO 2 optimizes luminance, yielding better outcomes. These results emphasize the importance of optimizing encapsulation materials and structures to enhance OLED performance.