This document analyzes the absorption losses of silver back reflectors in ultra-thin crystalline silicon solar cells using frequency domain finite difference simulations. It finds that for flat cells, losses are from intrinsic absorption, guided mode resonance, and plasma oscillations. For textured cells, losses are from guided mode resonance and plasma oscillations. Simulation results show multiple absorption peaks for both TE and TM modes in textured cells, with losses generally higher for TM modes. The study aims to improve light absorption in the thin active layers.