The effect of mode excitations on the absorption enhancement for silicon thin film solar cells

Abstract

Periodic gratings on solar cell back reflectors are an alternative to randomly textured surfaces to provide absorption enhancement. Theoretically, it is impossible to excite quasi-guided modes at every wavelength for a given grating geometry and the broad band enhancement can only be achieved by strong absorption peaks at several wavelengths. Therefore, the critical issue is how to maximize the short circuit current using a limited number of discrete quasi-guided modes. In this work, a common dielectric-semiconductor-dielectric-metal solar cell structure is investigated. It is found that although the number of guided mode peaks has pronounced effect on the solar cell short circuit current, the geometry resulting in the highest short circuit current does not coincide with the geometry leading to the most supported modes. It is also found that high-Q modes are always resulted from global optimization for TE incidence, while low-Q modes are resulted for TM incidence on one-dimensional gratings without a dielectric spacer. Besides, a properly designed and configured dielectric spacer can provide >40% improvement in short circuit current. It is therefore suggested for solar cells with metallic back reflectors, dielectric spacer should be included, and the texture should be formed on the dielectric spacer itself rather than on the metal. Finally, the optimization of the mode quality is proved to be critical in all cases, in addition to the number of supported modes. V

Aperiodic and randomized dielectric mirrors: alternatives to metallic back reflectors for solar cells

“…9(c) can provide the strongest light scattering and the largest scattering angle θ scatt . Nonetheless, the strong metallic absorption in Table 2 is the physical reason for low AM1.5 integrated absorbance, as verified by Lin et al [38]. The configuration in Fig.…”

“…In the case of a bare metallic back reflector with grating in Fig. 6(b), metallic absorption generally outperforms surface plasmon emission [38]. For the planar metallic back reflector in Fig.…”

“…In fact, it has been shown that the planar metallic mirror with grating on the dielectric spacer in Fig. 6(a) is more appropriate for solar cell absorption enhancement [38]. This is due to the fact that plasmon absorption loss can be generally lower for the planar metal-dielectric interface.…”

“…The configuration in Fig. 9(a) can provide a very small metallic absorption loss due to the planar metal-semiconductor interface, and it has been shown this is the preferred configurations [38] for high integrated absorbance. On the other hand, Fig.…”

Approaching conversion limit with all-dielectric solar cell reflectors

“…1(a-2) is not as efficient as Fig. 1(a-3) where the structure is a planar metallic mirror with a textured dielectric spacer [47]. The flat metal reflector with a textured dielectric layer illustrated in Fig.…”