Crystalline silicon (c-Si) solar cells are widely recognized due to its application in commercially available solar modules, and, also for representing more than 85% of the world PV cell market. However, the c-Si solar cells suffer with the efficiency loss due to indirect bandgap. For a single-junction c-Si cell, the theoretical efficiency calculated using Shockley–Queisser limit (SQ limit) is ηtheor≈ 29.1% (Eg = 1.1 eV) whereas the actual efficiency is only 26.7% (laboratory scale). A high efficiency (3rd generation) Tandem solar cell made by stacking two cells in series i.e., a cSi heterojunction cell as the bottom cell and a high bandgap (e.g., inorganic-organic perovskite, CIGS) cell as top cell, has the potential to surpass the efficiency beyond SQ limit. However, the tandem cells also suffer from absorption losses (leading to efficiency loss) due to; (a) the top cell mostly uses high bandgap polycrystalline material (e.g. perovskite or CIGS) for absorber layer which can only be grown with device quality on a planar surface, (b) the heterojunction cell at bottom side in tandem use a flat front surface instead of textured surface, used in single junctions for high efficiency, and, (c) compared to a single junction polycrystalline cell, the top cell of the tandem is without a metal back reflector, resulting in low current density. To overcome these absorption losses, we propose two-sided approach; (1) implement a new light management and (2) introduce new type of absorber layer. Thus, in the present work to address the first issue, we want to design a nanostructured layer which is Topologically Flat but Optically Rough (TFOR) and incorporate in the intermediate region (between top and bottom cell) for light trapping. For the second issue, we plan to use a material with high absorption coefficient. The reference bottom heterojunction cells (SHJ) are of indirect bandgap nature and hence use textured surface to increase light absorption. We want to replace it with quantum dot (QD) solar cell which are of direct bandgap nature. To that end, we will develop SiGe alloy nanocrystals (NC) which can be accommodated as the bottom cell (QD solar cell) of tandem solar cell.