Advanced optical design of tandem micromorph silicon solar cells

The role of refractive index of an interlayer in micromorph silicon solar cell is analyzed by means of optical simulations. Significant increases in quantum efficiency and photocurrent of the top cell are revealed for small refractive indexes of the interlayer (n < 2.0). At the same time a noticeable decrease in the performance of the bottom cell is observed. Optimization of thickness and refractive index of a single-layer antireflective coating (ARC) on glass is carried out in order to obtain maximal photocurrent either in the top or in the bottom cell. Moderate increases in photocurrents are obtained (up to 4%) for optimized ARC parameters. Potential thickness reductions of the absorber layers related to (i) an interlayer with small refractive index, (ii) an optimal ARC and (iii) enhanced light scattering are determined and compared. Among the three advanced optical designs, the greatest potential in thickness reduction (up to 50%) is associated with enhanced light scattering.