Exceptional Hole‐Selective Properties of Ta₂O₅ Films via Sn⁴⁺ Doping for High Performance Silicon Heterojunction Solar Cells

Abstract Carrier‐selective passivating contacts using transition metal oxides (TMOs) have attracted great attention for crystalline silicon (c‐Si) heterojunction solar cells recently. Among them, tantalum oxide (Ta₂O₅) exhibits outstanding advantages, such as a wide bandgap, good surface passivation, and a small conduction band offset with c‐Si, which is typically used as an electron‐selective contact layer. Interestingly, it is first demonstrated that solution‐processed Ta₂O₅ films exhibit a high hole selectivity, which blocks electrons and promotes hole transport simultaneously. Through the ozone pre‐treatment of Ta₂O₅/p‐Si interface and optimization of the film thickness (≈9 nm), the interfacial recombination is suppressed and the contact resistivity is reduced from 178.0 to 29.3 mΩ cm². Moreover, the Sn⁴⁺ doping increases both the work function and oxygen vacancies of the film, contributing to the improved hole‐selective contact performance. As a result, the photoelectric conversion efficiencies of Ta₂O₅/p‐Si heterojunction solar cells are significantly improved from 14.84% to 18.47%, with a high thermal stability up to 300 °C. The work has provided a feasible strategy to explore new features of TMOs for carrier‐selective contact applications, that is, bipolar carrier transport properties.