Optical and Electrical Analysis of Tandem Micromorph Silicon Solar Cell to Achieve Record-High Efficiency

Optical and electrical analysis of a micromorph silicon solar cell is carried out using numerical simulations. Electrical analysis reveals that generated charge carriers in p-doped amorphous silicon contribute to short-wavelength quantum efficiency of the top cell. In the bottom cell, non-ideal extraction of charge carriers from a few micrometer thick microcrystalline absorber is indicated. Improvements of optical and electrical properties are investigated in order to achieve high conversion efficiency of the solar cell. Potential for short-circuit current above 16 mA/cm² is indicated already for relative thin absorbers. Introduction of a (hypothetical) wavelength-selective intermediate reflector (interlayer) results in further improvements in the short-circuit current of the top and bottom cells in comparison to the optimised single interlayer. The interlayer is very important for high absorption especially in the top cell, while for the absorption in the bottom cell a broad angular distribution function of scattered light is of great importance. By optimising electrical parameters of the layers in the top cell (larger energy band-gap, buffer layers), open-circuit voltage of the solar cell is increased. The efficiency over 15 % is obtained in simulations for an optically and electrically optimised micromorph solar cell