Designing a solution-processable electron transport layer for transparent organic light-emitting diode

In this work, the extensively used opaque metal cathodes of the conventionally structured OLEDs were replaced with the widely used transparent electrode indium tin oxide (ITO) for solution-processed transparent organic light-emitting diode (T-OLED). A new solution-processable electron transport layer (ETL), aside from facilitating the efficient injection of electrons into the T-OLED, protected the organic emission layer (EML) of the T-OLED against the plasma damage during top ITO cathode sputter deposition. The newly designed solution-processed ETL was the composite of the zinc oxide nanoparticles (ZnO-NPs), and cesium carbonate-doped ethoxylated polyethyleneimine (d-PEIE) with the semi-hydrophilic poly (methyl methacrylate) (PMMA) interlayer coated on the EML insured the good wettability and contact of the hydrophilic ETL with the hydrophobic EML. The solution-processed T-OLED emitted the total maximum luminance of about 2417 cd/m² (bottom side emission at 1455 cd/m² and top emission at 962 cd/m²), total maximum current efficiency at 3.12 cd/A (bottom and top emissions at about 1.78 and 1.34 cd/A, respectively), and total maximum power efficiency at 1.64 l m/W (bottom and top emissions at about 0.95 and 0.69 l m/W, respectively) while having a very high optical transmittance of around 85% at 550 nm light wavelength.