Non‐Stoichiometric AlO x– Modified Al‐Doped MoO x Passivating Contacts Enabled High‐Efficiency Dopant‐Free Silicon Solar Cells

ABSTRACT Transition‐metal oxides such as MoO x are attractive hole‐selective contacts for crystalline silicon (c‐Si) photovoltaics; however, their performance is fundamentally limited by oxygen‐vacancy–induced work‐function instability, interfacial Fermi‐level pinning, and insufficient carrier selectivity. Here, we present a synergistic bulk–interface engineering strategy that combines Al‐incorporated MoO x (Al–MoO x ) with an ultrathin atomic‐layer‐deposited (ALD) AlO x interlayer to concurrently regulate Mo–O coordination, suppress defect‐mediated recombination, and restore interfacial band bending. Al incorporation homogenizes the electronic structure of MoO x and improves nanoscale carrier transport, while the AlO x interlayer provides effective chemical and field‐effect passivation, stabilizing the macroscopic potential offset at the c‐Si/oxide interface. Infrared spectroscopy and THz near‐field images reveal that AlO x passivation selectively enhances the low‐frequency electromagnetic response of thin Al–MoO x films, whereas this effect becomes negligible in thicker layers, consistent with an interfacial modulation of low‐frequency dielectric screening. As a result, p‐Si solar cells employing a 5‐nm Al–MoO x contact with a 6‐cycle AlO x interlayer achieve a power conversion efficiency of 23.24%, representing the highest reported efficiency for MoO x ‐based hole‐selective contacts without doped amorphous silicon. This work establishes a generalizable interface‐stabilization strategy for ultrathin oxide contacts in high‐efficiency silicon photovoltaics.