Coupling Incident Light to Guided Modes in Thin-Film Tandem Solar Cells With Intermediate Reflector

We investigate the impact of intermediate reflectors on textured thin-film tandem solar cells. The electric near-field intensity distribution inside the layer stack is simulated by rigorous scattering theory. From those results, we extract the angular scattering intensity distribution in the top and bottom solar cell. The improvement in top cell quantum efficiency for various different intermediate reflectors is correlated with the coupling efficiency to leaky waveguide modes for a periodic triangular grating as a model system. In a further step, we show that the same approach can be applied to randomly textured substrates where light couples to a broad distribution of waveguide modes. The integrated scattering intensity above the critical angle of total internal reflection of this system is successfully correlated with the measured external quantum efficiency of tandem solar cells with various IRs. A local investigation of trapped light is presented to identify good light-trapping structures.