Figure 3. Device performance of graphene-based OLEDs under study.

(a–c) EQE (a) power efficiency (b) and current efficiency (c) versus luminance characteristics of graphene-based OLEDs with and without TiO₂ under-layers. The data for ITO-based control OLEDs are also shown for comparison. All the devices in this figure contain GraHIL as low-index hole-injection layers and are based on glass substrates. In (a–c) legends with (L), (M) and (L,M) correspond to the data obtained with a half-ball lens attached, with a multi-junction architecture, and with both a multi-junction architecture and a half-ball lens, respectively. (d) Current density (J)–voltage (V)–luminance (L) characteristics. The detailed structure and J–V–L characteristics of a multi-junction device are represented in Supplementary Fig. 7. (e) The picture of an OLED with the proposed TiO₂/graphene/GraHIL electrode in operation. For the devices with TiO₂, d_TiO2 was fixed at 55 nm and d_org was chosen as the optimal condition for maximum EQE. For the devices without TiO₂ and the ITO-based devices, d_org was set at the same value as that of the corresponding devices with TiO₂.