Plasmonic scattering nanostructures for efficient light trapping in flat CZTS solar cells

摘要

CZTS (Cu_2ZnSnS_4) is a promising absorbing layer in photovoltaic devices, due to it is low cost, abundancy, and non-toxicity. However, recent developments in CZTS solar cells showed efficiency reaching barely over 9%. The low efficiency of CZTS solar cells is the main obstacle for replacing conventional high cost bulk silicon photovoltaic with CZTS solar cells. Herein, we propose an alternative route for enhancing the efficiency of CZTS solar cells by using plasmonic scattering nanostructures on the top surface of the CZTS active layer. Metamaterial and plasmonic nanostructures can confine, absorb, guide or scatter incident light in the nanoscale. Each one of these phenomena totally depends on the material type, shape, and geometrical dimensions of the used nanostructures. Therefore, theoretical study of different shapes and materials can guide the highest performance of desired phenomena. In this work, we studied the effect of changing plasmonic metal nanopyramids height, periodicity, and tapering angle on light scattering inside active layer of the CZTS solar cells. By sweeping pyramids height from 100nm to 300nm, periodicity of closed nanopyramids from 100nm to 180nm, and using pyramid base length 25nm, 50nm, 75nm, we found good enhancements in light absorption inside the active layer over reference planar CZTS structures. Each plasmonic CZTS solar cell structure is designed and analyzed using there dimensional (3D) finite element method (FEM) simulations. Using periodic boundary condition for simulating a smaller cell, and with mesh size is ten times smaller than lowest simulated wavelength. Input port energy came from air mass 1.5 sun light over wavelength range from 300nm to 800nm. Also, we studied effect of replacing molybdenum with refractory plasmonics titanium nitride (TiN). TiN is a promising plasmonic material as it has a similar plasmonic properties to gold at visible wavelength. After using TiN, we found also enhancements in light absorption. These interesting results could open a new way of integrating plasmonic scattering nanostructure inside flat CZTS solar cell for higher efficiency.