Potential of optical design in tandem micromorph silicon solar cells

Abstract

The potential of three advanced optical designs in tandem micromorph silicon solar cells are analysed by means of optical simulations: enhanced light scattering, intermediate reflector (interlayer) and antireflective coating (ARC) on glass. The effects on quantum efficiency, QE, and short circuit current density, JSC, of the top and bottom cell are investigated. In case of enhanced light scattering, the role of haze parameter and angular distribution function of scattered light is analysed separately. High haze parameter improves light trapping in top and bottom cell. However, the improvement in QE and JSC of the bottom cell is limited at higher haze parameters due to increased absorption in top cell and increased optical losses in realistic textured ZnO/Ag back contact. Broad ADF plays an important role for improving the performances of both, top and bottom cell. The role of refractive index of an interlayer between top and bottom cell is analysed. Significant increases in QE and JSC of the top cell are revealed for small refractive indexes of the interlayer (n < 2.0). At the same time noticeable decrease in the performance of the bottom cell is observed. Optimisation of thickness and refractive index of a single-layer ARC on glass is carried out in order to obtain maximal JSC either in top or in bottom cell. Moderate increases in JSC and QE are obtained for optimised ARC parameters. Among the three optical designs, the greatest potential, considering the improvements in both cells, is revealed for enhanced light scattering.