Graphene-on-Silicon Near-Field Thermophotovoltaic Cell

A graphene layer on top of a dielectric can dramatically influence the ability of the material for radiative heat transfer. This property of graphene is used to improve the performance and reduce costs of near-field thermophotovoltaic cells. Instead of low-band-gap semiconductors it is proposed to use graphene-on-silicon Schottky photovoltaic cells. One layer of graphene absorbs around 90% of incoming radiation and increases the heat transfer. This strong absorption is due to the excitation of plasmons in graphene, which are automatically tuned in resonance with the emitted light in the midinfrared range. The absorbed radiation excites electron-hole pairs in graphene, which are separated by the surface field induced by the Schottky barrier. For a quasimonochromatic source the generated power is one order of magnitude larger and the efficiency is on the same level as for semiconductor photovoltaic cells.

Figure 1

(a) Schematic representation of the TPV element. (b) Energy diagram for the Schottky graphene-on-Si diode working as an infrared PV cell.

Figure 2

(a) The theoretical limit on the operating voltage (ideal) and the voltage maximizing $P_{\mathrm{PV}}$ for the GOS cell as functions of $T_s$. (b) The radiative (blue) and absorbed in graphene (red) powers as functions of temperature. The output power for the GOS cell and InSb cell are presented as black and gray curves, respectively. (c) Efficiency of the TPV elements as a function of temperature. (d) Dependence of the scaled output power on the distance for different thicknesses of the ${\mathrm{SiO}}_2$ layer on Si including bare substrate.

Figure 3

(left) The output power at $d=10\mathrm{nm}$ as a function of temperature for different barrier heights. The curves 1, 2, and 3 correspond to the barriers 0.18, 0.28, and 0.33 eV, respectively. The emitter resonance frequency is 0.02 eV higher in all cases. The gray curve shows the result for InAs PV cell. (right) Fraction of the incident radiation absorbed in the graphene layer for different barrier heights.