Due to the unique microstructure of hydrogenated nanocrystalline silicon oxide (nc-SiO_x:H), the optoelectronic properties of this material can be tuned over a wide range, which makes it adaptable to different solar cell applications. In this work, the authors review the material properties of nc-SiO_x:H and the versatility of its applications in different types of solar cells. The review starts by introducing the growth principle of doped nc-SiO_x:H layers, the effect of oxygen content on the material properties, and the relationship between optoelectronic properties and its microstructure. A theoretical analysis of charge carrier transport mechanisms in silicon heterojunction (SHJ) solar cells with wide band gap layers is then presented. Afterwards, the authors focus on the recent developments in the implementation of nc-SiO_x:H and hydrogenated amorphous silicon oxide (a-SiO_x:H) films for SHJ, passivating contacts, and perovskite/silicon tandem devices.

To increase the efficiency in p-type wafer-based silicon heterojunction (SHJ) technology, one of the most crucial challenges is the achievement of excellent surface passivation. Herein, chemical passivation techniques known for n-type technology are successfully applied on p-type float–zone (FZ) wafers, and wafer surface passivation quality is correlated with parameters from plasma diagnostics, namely crystallization rate and electron temperature indices. It is shown that plasma ignition at higher powers than deposition powers enhances effective minority carrier lifetimes τ_eff fourfold for p- (0.6–2.1 ms) and sixfold for n-type (0.6–3.2 ms) wafers while giving opportunity to process under lower electron temperature indices during the nucleation phase. A subsequent hydrogen plasma treatment has a further beneficial effect on chemical passivation, leading to high effective minority carrier lifetimes of 4.5 and 3.1 ms, and implies open-circuit voltages, i-V_OC, of 735 and 720 mV for p- and n-type wafers, respectively. In particular, cell precursors built on p-type wafers demonstrate excellent surface passivation with τ_eff and i-V_OC (4.1 ms and 745 mV). Using these process optimizations, SHJ cells on both p- and n-type wafers are fabricated with efficiencies exceeding 21%.