Optimisation of the Back Surface Reflector for Textured Polycrystalline Si Thin Film Solar Cells

Abstract

The back surface reflector of a solar cell not only enhances back reflection, but also may contribute to further randomising light. In this paper, three different types of back surface reflectors (dielectric/metal bi-layer, pigmented diffuse reflector and Ag nanoparticles) are investigated and compared with one another to determine the optimal for polycrystalline Si (poly-Si) thin film solar cells grown on textured glass superstrates. The optimal dielectric layer material and thickness of an interposed dielectric layer between Si and metal contact is optimised via WVASE simulation for ∼2μm random textured poly-Si thin film solar cells on glass. Experimentally, the Si thin films are deposited on Aluminium Induced Textured (AIT) glass and those with optical absorption close to Lambertian limited absorption are selected for investigation. The experiment confirms the simulation results and finds the best back reflector configuration— 500 nm MgF2+Ag. Theoretically Ag nanoparticles on the rear surface of a cell should induce surface plasmon effects, scattering light obliquely into the Si film. However, this work indicates that Ag nanoparticles degrade Jsc of textured poly-Si thin film solar cells. The reason why Ag nanoparticles do not work on textured poly-Si thin film solar cells needs further investigation.