Silk Fibroin‐Based Flexible Organic Light‐Emitting Diode with High Light Extraction Efficiency

Abstract It is an essential issue for the efficiency of flexible organic light‐emitting diodes (OLEDs) to be improved in display and lighting applications. Herein, the use of silk fibroin (SF) as a flexible OLED substrate with enhanced light extraction efficiency (LEE) is reported. Regenerated SF is prepared via a casting method and then coated with conductive indium tin oxide (ITO) via magnetron sputtering. SF‐based flexible OLED outperforms its reference device in terms of turn‐on voltage, peak brightness, and LEE, where glass and polyethylene terephthalate are used as rigid and flexible substrates, respectively. The improved device performance can be ascribed to the low refractive index of SF and its lower surface roughness and more matched energy levels compared to those of other substrates, resulting in a high LEE. Notably, a molecular dipole layer can be formed between the interface of ITO and SF. The dipole moment pointing to the ITO surface effectively changes the ITO work function and reduces the potential barrier height for hole transfer. The work provides new ideas for constructing high‐performance OLEDs on biomass‐based substrates with excellent flexibilities and high LEEs.