Sn-Doped Nb₂O₅ Films as Effective Hole-Selective Passivating Contacts for Crystalline Silicon Solar Cells

Carrier-selective contacts (CSCs) in crystalline silicon (c-Si) solar cells have attracted great attention due to suppressing contact region recombination and achieving higher conversion efficiency. Among transition metal oxides for CSCs, niobium oxide (Nb2O5) is considered as an attractive candidate for electron-selective contact due to its excellent passivation properties and small conduction band offsets with c-Si. Nevertheless, the performance of c-Si solar cells employing Nb2O5 contact layer has not been explored yet. Herein, the carrier selectivity of solution-processed Nb2O5 films is investigated for c-Si. Interestingly, Nb2O5 exhibits high electron-blocking performance and low contact resistivities with p-Si. The ultra-thin SiOx interlayer formed by UV-O-3 pretreatment further reduces the contact resistivities and increases minority carrier lifetime due to the improved contact interface. The Sn4+ doping improves the work function of Nb2O5 to induce larger upward band bending at c-Si surface, thus enhancing the hole selectivity. As a result, p-type c-Si solar cells with solution-processed Nb2O5 hole-selective contact layer have achieved the highest power conversion efficiency of 18.4%, with a high-thermal stability superior to the typical hole transport layers. This work first demonstrates the exceptional hole selectivity of Nb2O5, which shows very promising applications in high-efficiency c-Si solar cells.