In the context of valley- and spintronics, the semiconducting 2D transition metal dichalcogenides (TMDs) constitute an interesting research platform due to their unique combination of spin- and valley-polarized band edges which allow for optically addressing two distinct valley states with circularly polarized light. So far, it has been shown that optically excited, valley-polarized states such as excitons and trions can further lead to a valley polarization of free charge carriers in TMDs with lifetimes in the ns range as an important step towards opto-electronic devices. While this mechanism is accessible in monolayers of WSe2, it is not in the case of MoSe2. Here, we show that a combination of these two materials into a heterobilayer not only enables the transfer of a valley polarization of free charge carriers from WSe2 to MoSe2, but that the additional incorporation of an atomically thin spacer layer of hBN further enhances this transfer.