Light trapping schemes in organic solar cells: A comparison between optical Tamm states and Fabry-Perot cavity modes

摘要

Recently optical Tamm states at metal/photonic crystals interface have been applied in thin-film organic solar cells (OSCs) as a new light trapping scheme for photon absorption enhancement. In this work, we theoretically investigate this scheme thoroughly to optimize the absorption performance for such optical Tamm states based OSCs (OTS-OSCs). We find that the overall absorptivity of the OTS-OSCs can be improved by using photonic crystals bilayers with a higher refractive index contrast, which is a result of the more strongly enhanced field intensity in the active layers. The conventional Fabry-Perot cavity modes based OSCs (FP-OSCs) are also studied for comparison, whose absorption performance is found to be strongly dependent on the refractive index of the additional dielectric layer. These two schemes based OSCs exhibit comparable absorption performance in aspects of absorption enhancement, field distributions, and angle effect in the planar case. However, the proposed OTS-OSCs exhibit ～10% higher overall absorptivity than that for the FP-OSCs in the corrugated case, if both OSCs exhibit the same overall absorptivity in the planar case. The reduced absorption in the corrugated FP-OSCs is a result of the strong scatterings induced losses in the metal, which can be avoided by the photonic crystals bilayers in the OTS-OSCs. Therefore, the proposed Tamm states based scheme shows a higher value in corrugated OSCs.