Universal high work function flexible anode for simplified ITO-free organic and perovskite light-emitting diodes with ultra-high efficiency

Flexible transparent electrode materials such as conducting polymers, silver nanowires, carbon nanotubes and graphenes are being investigated as possible replacements for conventional brittle inorganic electrodes. However, they have critical drawbacks of low work function (WF), resulting in a high hole injection barrier to an overlying semiconducting layer in simplified organic or organic–inorganic hybrid perovskite light-emitting diodes (OLEDs or PeLEDs). Here, we report a new anode material (AnoHIL) that has multifunction of both an anode and a hole injection layer (HIL) as a single layer. The AnoHIL has easy WF tunability up to 5.8 eV and thus makes ohmic contact without any HIL. We applied our anodes to simplified OLEDs, resulting in very high efficiency (62% ph el−1 for single and 88% ph el−1 for tandem). The AnoHIL showed a similar tendency in simplified PeLEDs, implying universal applicability to various optoelectronics. We also demonstrated large-area flexible lightings using our anodes. Our results provide a significant step toward the next generation of high-performance simplified indium tin oxide (ITO)-free light-emitting diodes. Flexible transparent electrode materials, including conducting polymers, silver nanowires, carbon nanotubes, and graphene, have been investigated to replace conventional brittle indium tin oxide (ITO). However, they have serious problems of low work function (WF), resulting in a high hole injection barrier to overlying semiconducting layers. Now, Tae-Woo Lee from Seoul National University in Korea and co-workers have developed ITO-free simplified organic and perovskite light-emitting diodes with high-efficiency by using a single-layered high WF polymeric anode, which can act as both an anode and a hole injection layer. Since the high WF polymeric anode make efficient hole injection to the overlying organic and perovskite semiconducting layers, they dramatically improve the device efficiencies even without any hole injection layer. We report a new anode material that has multifunction of both an anode and a hole injection layer (HIL) as a single layer. Our anode has easy work function tunability up to 5.8 eV and thus makes ohmic contact without any HIL. We applied our anodes to simplified organic light-emitting diodes, resulting in high efficiency (62% ph el−1 for single and 88% ph el−1 for tandem). Our anode showed a similar tendency in simplified perovskite light-emitting diodes. We also demonstrated large-area flexible lightings using our anodes. Our results provide a significant step toward the next generation of high-performance simplified light-emitting diodes.