Abstract
We have investigated the impact of three types of intermediate reflectors on the absorption enhancement in the top cell of micromorph tandem solar cells using rigorous diffraction theory. As intermediate reflectors we consider homogenous dielectric thin-films and 1D and 3D photonic crystals. Besides the expected absorption enhancements in cases where photonic band gaps are matched to the absorption edge of the semiconductor, our results distinguish between the impact of zero order Bragg-resonances and diffraction-based enhancement at larger lattice constants of the 3D photonic crystal. Our full-spectrum analysis permits for a quantitative prediction of the photovoltaic conversion efficiency increase of the a-Si:H top cell.
Highlights
The micromorph solar cell which we analyze in the present work consists of two different absorbing layers: amorphous silicon (a-Si:H) is the top and microcrystalline silicon is the bottom cell [1]
We have investigated the impact of three types of intermediate reflectors on the absorption enhancement in the top cell of micromorph tandem solar cells using rigorous diffraction theory
Besides the expected absorption enhancements in cases where photonic band gaps are matched to the absorption edge of the semiconductor, our results distinguish between the impact of zero order Bragg-resonances and diffraction-based enhancement at larger lattice constants of the 3D photonic crystal
Summary
The micromorph solar cell which we analyze in the present work consists of two different absorbing layers: amorphous silicon (a-Si:H) is the top and microcrystalline silicon (μc-Si) is the bottom cell [1]. The diffractive effect causes a prolongation of the optical path and enhanced so the number of absorbed photons [14] It permits to excite guided modes which allow to enhance absorption tremendously over a narrow spectral domain. In the present contribution we aim at elucidating the impact of various approaches for IRL on the absorption enhancement in the top cell of a tandem cell with rigorous diffraction theory For this purpose we evaluate the spectrally dependent absorbance, based on material data of a-Si:H, as deposited for thin-film solar cells. This permits for an estimation of the enhancement of the number of absorbed photons when compared to the tandem cell without IRL. We present here a quantization of this enhancement for the three IRL on a-Si:H thin-film top cells
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