In this paper, we present investigations on the development of a new type of interfaces for silicon heterojunction solar cells, namely silicon oxide buffer layers, leading to the formation of p-doped amorphous silicon/ silicon oxide/ n-doped crystalline silicon structures. First, the new cell concept is evaluated thanks to numerical simulations of the electrical (charge carrier transport) and optical (light absorption in c-Si) behaviour. Provided that the barrier remains low and thin enough, tunneling allows for the extraction of the photo-generated charges; the insertion of a thin silicon oxide layer has no influence on light absorption in c-Si, hence on the short circuit current, contrary to amorphous silicon. Then, heterojunction solar cells with an interfacial silicon oxide layer are fabricated using oxidation of the crystalline silicon wafer surfaces in pure deionized hot water. Interfaces with silicon oxide lead to an increase of the passivation quality because of an increased negative fixed charge; the resulting open-circuit voltage is above the one reached in cells with no buffer layer. Interestingly, no strong decrease of the fill factor is observed, suggesting that there is no formation of a tunnel barrier.