Strategy for One‐Step Optimization of Metal Oxide Passivating Contact Materials for Si Heterojunction Solar Cells through Growth Angle Variation

High-efficiency silicon (Si) heterojunction (SHJ) solar cell technology is currently limited by multi-step fabrication protocol required for optimal passivation and carrier selectivity. Here, a novel, one-step oblique-angle reactive sputtering strategy is presented that leverages angle-dependent ion-bombardment to simultaneously tailor the bulk and interfacial properties of metal oxide contact material on Si via in situ ion assisted oxidation. Using vanadium oxide (V₂O_5-x) as a model system, it has been demonstrated that the deposition at a glancing angle of 80° yields a phase-pure, high-work-function V₂O_5-x film-essential for field effect passivation, while also facilitating stoichiometric improvement of the retained native silicon oxide layer on Si surface. An intermediate growth angle of 40°, produces a mixed-phase V₂O_5-x film, without compromising interfacial quality. Monte Carlo simulations, supported by time-of-flight secondary ion mass spectrometry data, reveal that growth angle governs the V-Si-O intermixing depth across the interface through variations in ion incidence geometry and energy deposition profile, critically influencing the interfacial layer properties. This simple, one-step, room temperature, angle-tuned reactive sputtering method circumvents multi-step chemical pre-treatments of the silicon surface and offers a viable pathway for integrating carrier selective metal oxides in SHJ solar cells, with broader applicability across silicon-based electronic and optoelectronic devices.