Combined perovskite/crystalline-silicon four-terminal tandem solar cells promise >30% efficiencies. Here we propose all-thin-film double-junction architectures where high-bandgap perovskite top cells are coupled to ultrathin c-Si bottom cells enhanced with light trapping. A complete optoelectronic model of the devices was developed and applied to determine the optimal intermediate layers, which are paramount to maximize the cells’ photocurrent. It was ascertained that by replacing the transparent conductive oxides by grid-based metallic contacts in the intermediate positions, the parasitic absorption is lowered by 30%. Overall, a 29.2% efficiency is determined for ∼2 um thick tandems composed of the optimized interlayers and improved with Lambertian light trapping.