Transparent Hole-Selective Molybdenum Oxide Passivating Contact with Chlorine-Based Interlayer Enabling 22.5% Efficient Silicon Solar Cells

The need to increase transparency in existing passivating contacts for crystalline silicon solar cells has motivated the development of transparent contacts based on transition metal oxides (TMOs). Among hole-selective materials, molybdenum oxide (MoO_x) has achieved the greatest success so far. However, despite providing low contact resistivity, MoO_x relies on an intrinsic hydrogenated amorphous silicon (a-Si:H(i)) interlayer to achieve high levels of surface passivation and thus high open-circuit voltage at a device level, partially defeating the objective of improved transparency. Herein, we report unprecedented performance for a-Si:H-free MoO_x-based contacts by employing an alternative passivating interlayer based on a well-engineered chlorine-containing Al-alloyed titanium oxide/titanium dioxide (Al_yTiO_x/TiO₂)stack. The resulting Al_yTiO_x/TiO₂/MoO_x stack achieved record levels of passivation, reaching J₀ values as low as 16 fA cm⁻², closer to values reported for a-Si:H-based contacts, while maintaining lower contact resistivity, well below 100 mΩ cm⁻². Additionally, the stack presents improved transparency compared to a-Si:H-based contacts, with gains in short-circuit current density of at least 0.8 mA cm⁻². The work pushes the performance of hole-selective passivating contacts based on TMOs to new levels, enabling a record efficiency of 22.53% for cells with fully transparent hole-selective passivating contacts. This work serves as an important stepping stone toward low-thermal-budget, simple manufacturing of high-efficiency solar cells.