Performance investigation of tandem nano-gap thermophotovoltaic system considering the near-field thermal radiation

In this paper, a near-field thermophotovoltaic (TPV) system with a dual TPV cell design is considered and studied numerically. The fluctuational electrodynamics accompanied by the dyadic Green's function are utilized for calculating the radiation heat flux. The generated photocurrent and the conversion efficiency are obtained by solving the photon-coupled charge transport equations. It was discovered that the addition of the second TPV cell to the system, increases the generated photocurrent of the system due to the absorption of the low-energy photons and generation of the electron-hole pairs. By increasing the gap size between the emitter and Si TPV cell from 50 nm to 1 mu m, the generated photocurrent decreases because of the reduction of the near-field thermal radiation effects. Finally, the tandem nano-gap TPV system shows higher conversion efficiency compared with the single Si TPV cell for different values of the vacuum gaps, and the gap size of d1 = 200 nm is the optimum gap size due to the improvement of the conversion efficiency of the system.