Conventional silicon heterojunction solar cells employ defects-prone a-Si:H layers for junction formation and passivation purposes. Substituting these layers with hole-selective MoO(x)and electron-selective TiO(x)can reduce parasitic absorption and energy band offsets issues associated with doped silicon films. In this work, dopant-free asymmetric heterostructure Si solar cells are studied with and without SiO(2)passivation layer, and their performance has been compared. The inclusion of ultrathin SiO(2)insulator as a passivation layer promotes significant band bending that induces interface inversion of crystalline silicon as well as maintains the electric field required to tunnel charge carriers. The energy band diagram studies and variation of oxide thickness show that the IV characteristics of the solar cell critically depend on the insulator thickness; as the carriers tunnelling through the insulator becomes negligible at larger thicknesses. The simulated structure with MoO(x)as front hole-selective contact and without any passivation exhibited conversion efficiency of 15.73%, which improved to 18.69% by incorporating passivated a-Si:H. However, by employing rear SiO2/TiO(x)stack with the front SiO2/MoOx, the device performance enhanced to open-circuit voltage of 785 mV, short-circuit current density of 41 mA/cm(2), fill factor of 77%, and simulated conversion efficiency of 24.83%, which is similar to 10% enhancement in the performance as compared to reference device employing traditional a-Si:H with dopant-free films.