Improving the efficiency of solar cells is one of the most straightforward approach to reduce the area-related balance of system costs of photovoltage power generation. For conventional and market dominating single-junction silicon solar cells, the laboratory record power conversion efficiency (PCE) of 26.6% is very approaching its theoretical limit of 29.4%, which makes it foreseeable that the room for further improvements is quite limited. In contrast, the monolithic perovskite/silicon tandem solar cells, which significantly increases the theoretical efficiency potential surpassing 45%, are considered a promising option to significantly enhance the efficiency and further reduce the photovoltage system costs. In order to enable further improvements in the efficiency of the perovskite/silicon tandem solar cells, a better understanding of the fundamental loss processes in tandems must be gained and appropriate concepts to suppress them must be established. This dissertation addresses the overall objective to optimise perovskite and silicon sub-cells as well as their interconnection for the application in tandems. For an efficient perovskite/silicon tandem solar cell, many critical issues, such as the choice of the recombination layer and the top transparent conductive electrode, the optimization of transparent perovskite top subcells and near-infrared responsive silicon bottom subcells, as well as the compatibility between perovskite and silicon subcells, need to be discussed and solved. In order to achieve an efficient recombination layer with a highly anisotropic film conductivity, an ultra-thin metal islands-based interconnection layer was introduced as an efficient photoanode for the excellent photoelectrochemical (PEC) water oxidation, exhibiting an excellent PEC performance with low onset potential (~ 0.88 V) and a high photocurrent density (~ 34 mA/cm2). The results suggest a promising strategy to develop highly efficient anisotropic conductive recombination layers for monolithic perovskite/Si tandem devices. Then, a MoOx/Ag/WOx (MAW) stack was presented as a promising oxide-metal-oxide (OMO) based transparent conductive electrode (TCE) to realize the high-performance semitransparent perovskite solar cell (PSC). The resulting MAW based semitransparent PSC exhibited a efficiency of as high as 15.40% with an average visible transmittance of = 10.17%, which is the highest AVT reported for ultra-thin metal film based semitransparent PSCs with the PCE above 15%. To further improve the performance of the semitransparent PSC, a sputtering deposited indium-zinc oxide (IZO) was employed to replace the OMO top electrode for the buffer layer free semitransparent perovskite solar cell. We demonstrated that the vacuum-evaporated electron-transport layer (ETL) of 1,10-phenanthroline (BCP) has a better sputtering bombardment tolerance compared to the solution-processed ETL of PCBM/BCP. By further optimizing the thickness of BCP and perovskite layers, the semitransparent device exhibited a efficiency of 16.23% as well as a high transmittance of 39.46% in the wavelength of 300 to 1200 nm. By employing the optimized semitransparent PSC as the top cell in a four-terminal perovskite/silicon tandem solar cell, a combined efficiency of 24.60% was achieved. Subsequently, a charge transfer induced BCP:Ag complex was further employed to mediate the electrical contact between a C60 electron-transport layer and sputtered IZO top electrode. We demonstrated that the multifunctional BCP:Ag complex can reduce the electron extraction barrier by pulling up the Fermi level of BCP, create beneficial gap states for electron transport, serve as a hole blocking layer to suppress charge recombination, and protect the C60 underlayer from the sputtering damage. As a result, the optimized electrical contact at the C60/BCP:Ag/IZO interface significantly recovered the FF of the semitransparent PSC from 71.8% to 80.1 %, yielding a device efficiency of 18.19%. By using a 23.19% efficient silicon solar cell, a four-terminal perovskite/silicon tandem configuration with a total efficiency of 27.59% was also achieved. Finally, for achieving monolithic perovskite/silicon tandem solar cells, the BCP:Ag buffer layer was also introduced to mediate the contact between the transparent conductive oxide (TCO) recombination layer and the tunnel oxide passivating poly-Si contact (TOPCon) based silicon bottom cell. We demonstrated that the BCP:Ag buffer layer can simultaneously prevent the TCO sputtering damage, improve the passivation of the TCO/TOPCon contact, and provide an excellent electron-conductive property. By implementing this efficient TCO/BCP:Ag recombination contact, a certified tandem efficiency of 25.2% was achieved, providing a promising way to develop high-performance monolithic perovskite/TOPCon tandem solar cells with TCO recombination layers. Key words: PVK/Si tandem device, recombination layer, transparent electrode, damage free, BCP:Ag complex.