The study of a two-terminal (2T) perovskite/c-Si tandem solar cell requires accurate and concurrent description of photons absorption and tunnelling-mediated charge transport. By analysing current collection across the device heterointerfaces, we investigated the effect of (i) perovskite thickness on the short-circuit current density (Jsc) of the tandem device and (ii) temperature on devices performance. We deployed an advanced opto-electrical modelling framework based on optical sub-models from GenPro4 and on self-consistent fundamental semiconductor equations implemented in TCAD Sentaurus. Using these simulations of perovskite/c-Si tandem solar cells, an in-depth analysis of the physics of current contribution of supporting layers has been carried out. Solving numerically the fundamental equations of semiconductors, we theoretically show for the first time that electron-hole pairs photo-generated in the TRJ can be collected, effectively boosting Jsc values well beyond (photocurrent density) Jph levels. In addition, a temperature-based study of these perovskite/c-Si tandem solar cells has been performed to evaluate the temperature coefficient which is useful for their energy yield simulations.