Solar cell design using graphene-based hollow nano-pillars.

In this paper, the full solar spectrum coverage with an absorption efficiency above 96% is attained by shell-shaped graphene-based hollow nano-pillars on top of the refractory metal substrate. The material choice guarantees the high thermal stability of the device along with its robustness against harsh environmental conditions. To design the structure, constitutive parameters of graphene material in the desired frequency range are investigated and its absorption capability is illustrated by calculating the attenuation constant of the electromagnetic wave. It is observed that broadband absorption is a consequence of wideband retrieved surface impedance matching with the free-space intrinsic impedance due to the tapered geometry. Moreover, the azimuthal and longitudinal cavity resonances with different orders are exhibited for a better understanding of the underlying wideband absorption mechanism. Importantly, the device can tolerate the oblique incidence in a wide span around 65°, regardless of the polarization. The proposed structure can be realized by large-area fabrication techniques.