Fig. 1 Schematic of a model device representative of a surface plasmon-enhanced OSC. The two-dimensional Ag grating electrode has a square lattice with a period of Λ_G, whose unit cell is drawn in red-dotted lines. The grating linewidth is 0.25Λ_G. The orientation of the Cartesian coordinates is shown, with O on the grating surface denoting the origin. Also shown are the directions of the wave vector (k) and electric field (E) of an incident plane wave.

Fig. 2 (a) Calculated absorption efficiency (η_abs) of the model device with t_org = 70 nm, t_u = 30 nm, t_a = 10 nm, and t_l = 30 nm, as a function of the grating period (Λ_G) and the wavelength (λ) of the incident light. The maximum of η_abs is 0.71. (b) The z-component of the electric field corresponding to point ‘a’ (λ = 680 nm, Λ_G = 380 nm) in (a). (c) The electric field intensity (|E|² = E · E^*) corresponding to point ‘a’. (d) The z-component of the electric field corresponding to point ‘b’ (λ = 760 nm, Λ_G = 320 nm). (e) The electric field intensity corresponding to point ‘b’. E₀ denotes the amplitude of the incident electric field. In (b) to (e), solid lines represent materials boundaries, and grating boundaries that do not lie on the planes shown are drawn as dotted lines.

Fig. 3 (a) Calculated absorption efficiency (η_abs) of the model device with t_org = 50 nm, t_u = 10 nm, t_a = 10 nm, and t_l = 30 nm, as a function of the grating period (Λ_G) and the wavelength (λ) of the incident light. The maximum of η_abs is 0.76. (b) The z-component of the electric field corresponding to point ‘a’ (λ = 660 nm, Λ_G = 380 nm) in (a). (c) The electric field intensity (|E|² = E · E^*) corresponding to point ‘a’. (d) The z-component of the electric field corresponding to point ‘b’ (λ = 760 nm, Λ_G = 320 nm). (e) The electric field intensity corresponding to point ‘b’.

Fig. 4 (a) Internal quantum efficiency (η_int) of the model device with t_org = 50 nm, t_u = 10 nm, and Λ_G = 320 nm versus γ ≡ t_a/L_d, calculated for different values of L_d and λ. The black solid line shows η_int calculated using Eq. (6). (b) Steady-state exciton density profile (n_exc) in the active layer when t_a = 3.5 nm, L_d = 5 nm, and λ = 760 nm. The top (z = 30 nm) and bottom (z = 33.5 nm) faces correspond to the UTL– and LTL–active layer interfaces, respectively, where at the former (or latter) interface the exciton dissociation velocity is zero (or infinite).

Fig. 5 (a) (Top) Absorption coefficient (α) of CuPc (red) and C₆₀ (blue). (Bottom) Absorption efficiency (η_abs), as a function of the grating period (Λ_G) and the wavelength (λ), of the active layer in the organic solar cell based on the CuPc and C₆₀ DA heterojunction. The maximum of η_abs is 0.74. (b) The z-component of the electric field corresponding to point ‘a’ (λ = 600 nm, Λ_G = 320 nm) in (a). (c) The z-component of the electric field corresponding to point ‘b’ (λ = 620 nm, Λ_G = 200 nm).

Fig. 6 (a) Short-circuit current density (J_sc) (red), solar-spectrum-weighted absorption efficiency (〈η_abs〉) (blue), and internal quantum efficiency (η_int) (black) versus γ = t_CuPc/L_CuPc = t_C60/L_C60 of the surface plasmon (SP)-enhanced CuPc–C₆₀ solar cell with t_org = 50 nm, and t_u = 5 nm. (b) External quantum efficiency (η_ext) of the optimized SP-enhanced device (red, γ = 1.0), compared with that of the optimized ITO-based device (black) consisting of: glass / 150 nm ITO / 5 nm PEDOT:PSS / 13 nm CuPc / 21 nm C₆₀ / 29 nm BPhen / 100 nm Ag.

Fig. 7 (a) Schematic diagram showing the orientation and polarization of an incident plane wave. An s-polarized (or p-polarized) plane wave whose electric field is drawn as a red (or blue) arrow has the electric (or magnetic) field vector perpendicular to the plane of incidence drawn as green dotted lines. (b) Schematic of a device considered to calculate the ergodic limit shown in (c), where an active layer is sandwiched between a perfect back reflector and an ideal front Lambertian surface with an ideal anti-reflection coating. (c) Short-circuit current density (J_sc) of the optimized SP-enhanced device in Sec. 4 versus incident polar angle (θ) for three azimuthal angles, ϕ = 0° (red), 22.5° (blue), and 45° (green). For comparison, J_sc of the optimized ITO-based device in Sec. 4 (brown) and the device shown in (b) (Ergodic limit, black open squares) are also shown. ‘+’ and ‘×’ symbols refer to s- and p-polarizations, respectively. The three black lines are $J_{\text{sc}}^{\text{max}}\text{cos}\theta$, where $J_{\text{sc}}^{\text{max}}$ is J_sc(θ = 0°) for each device.