Tapered Silicon Nanopillars for Enhanced Performance Thin Film Solar Cells

Silicon nanopillars and their ordered arrays are attractive structures for solar cell applications. Identifying the suitable geometry, for achieving an optimum antireflection property along with the formation of radial junctions, is presented in this paper. It is seen that tapered silicon nanopillars help in grading refractive index mismatch between air and silicon optimally. FDTD simulations of tapered silicon nanopillars having different height, diameters and period have been done using Lumerical FDTD Solutions® software for achieving the optimum optical and electrical characteristics. It is seen that three-fold advantage is obtained with the nanopillars optically. First, the nanopillars help in reducing the reflection ensuring a greater injection of the incident light. Second, they also enable enhanced light trapping due to multiple reflections from the nanopillar walls ensuring better absorption in the nanopillar itself. Finally, the nanopillars act as scattering objects ensuring enhanced absorption in the substrate housing the nanopillars. Further, if the dimensions of the tapered nanopillar are chosen optimally, an enhanced charge carrier collection is obtained due to the formation of radial junctions. A novel technique of using silica nanoparticles as the masking layer in the metal assisted chemical etching process has been proposed for realization of the optimized silicon nanopillars. An average reflection loss of ∼5% over the spectral range of 300-1100 nm is obtained due to the formation of nanopillars on silicon substrate.