The optical performance of tandem a-Si:H/mu c-Si:H (micromorph) thin film solar cell was investigated experimentally and by means of rigorous 3-D optical simulation. The interplay of intermediate reflectors, with different refractive indices and thicknesses, and front electrode surface texture was studied. Experiments and simulations show that LPCVD ZnO based front electrodes have the highest optical potential together with a low refractive index of the intermediate reflector. The intermediate reflector layer serves for redistribution of the mid-range solar spectrum between the top and bottom cell, while the sum of the top and bottom cell currents decreases with increasing IRL thickness. Additionally, promising concepts to increase the short-circuit current of the tandem solar cell are shown. The most important steps are related to lowering parasitic absorption in supportive layers by the introduction of silicon oxide layers and improving the light incoupling by introduction of anti-reflective layers. (C) 2014 Elsevier B.V. All rights reserved.