We present a concept for a core-shell silicon nanowire thin film solar cell showing perfect light trapping. Nanowires are wet chemically etched into a several µm thick laser-crystallized silicon thin film on glass. The nanowires are equipped with an a-Si heteroemitter deposited as a shell around the nano¬wires by PECVD to achieve a radial p-n heterojunction. The space between the nanowires is filled with ZnO:Al, acting as a trans-parent contact. Our core-shell nanowire solar cells reached an efficiency of 8.8%. The main emphasis of this work is on the optical properties of the nanowire solar cell system.