Optical simulations of P3HT/Si nanowire array hybrid solar cells.

An optical simulation of poly(3-hexylthiophene) (P3HT)/Si nanowire array (NWA) hybrid solar cells was investigated to evaluate the optical design requirements of the system by using finite-difference time-domain (FDTD) method. Steady improvement of light absorption was obtained with increased P3HT coating shell thickness from 0 to 80 nm on Si NWA. Further increasing the thickness caused dramatic decrease of the light absorption. Combined with the analysis of ultimate photocurrents, an optimum geometric structure with a coating P3HT thickness of 80 nm was proposed. At this structure, the hybrid solar cells show the most efficient light absorption. The optimization of the geometric structure and further understanding of the optical characteristics may contribute to the development for the practical experiment of the promising hybrid solar cells.

Theoretical consideration of III-V nanowire/Si triple-junction solar cells.

In this paper, we report theoretical consideration and simulation of a proposed III-V nanowire (NW)/Si triple-junction solar cell. The cell consists of two axially connected III-V NW subcells that are grown and electrically integrated on an active Si substrate. The optical properties of the cell are thoroughly analyzed by using the finite-difference time-domain method. It is found that NW subcells with optimized geometry have high absorption throughout their absorption region. Meanwhile, beyond the absorption edge of the top and middle NW subcells, the NWs act as an efficient antireflection coating for the bottom Si subcell due to the formation of an optical cavity within the NW layer. The physics responsible for the enhanced light harvesting process is qualitatively explained through modal analysis. In addition, we have shown that the condition of current matching in a III-V NW/Si multi-junction can be fulfilled by adjusting the diameter of the NWs. In order to study the current-voltage characteristics of the proposed cell, the optical generation profiles under AM1.5G illumination are incorporated into an electrical modeling. Our optoelectrical simulations indicate that, with an excellent current matching between subcells, the performance of the proposed structure is comparable with state-of-the-art multi-junction cells. The results presented here indicate that semiconductor NWs may provide a promising route toward high efficiency multi-junction solar cells.