Figure 3. Modification of absorption and emission results in an ideal PV nanostructure achieving >40% power conversion efficiency.

Emission and absorption for (a) slab without back reflector (i.e. light can escape through the back surface without reflection), (b) slab with back reflector, and (c) ideal nanostructured cell. The emission and absorption are represented in terms of their half-angle, θ. Absorption/emission over all angles (standard cell) corresponds to θ = 180°; however, the illumination from the sun is only over a subset of half-angles from 0 to θ_s. Thus, the mismatch between θ_s and θ_emit results in a decreased voltage. (d) I-V curves corresponding to the three structures (a–c). All structures are illuminated with the AM 1.5G spectrum and show increased V_oc as θ_emit→θ_s.