Figure 2. Synergetic optical effect of TiO₂ as a high-index layer and GraHIL as a low-index HIL.

(a,b) Calculated power dissipation spectra weighted with the emitter spectrum in arbitrary units (mapped as a colour defined in the colour bars.) versus in-plane wave vector: (a) with TiO₂ but without GraHIL; (b) with both TiO₂ and GraHIL. The black dashed lines indicate border lines dividing representative optical modes including outcoupled, substrate-confined (subs), waveguided (wg) and evanescent modes. (c) Calculated power dissipation versus normalized in-plane wave vector at λ=550 nm for various electrode structures under study. For the devices with TiO₂, d_TiO2 was fixed at 55 nm and d_org was chosen for optimal conditions in each case. For the devices without TiO₂, d_org was set at the same value as that of each counterpart in the devices with TiO₂.