Boosting Perovskite/Silicon Tandem Solar Cells with Dual-Gradient Tungsten-Doped Indium Oxide (IWO) Interlayers

The alignment of work function between transparent conducting oxides and charge transport layers is critical for the fill factor in perovskite/silicon tandem solar cells. Silvaco TCAD simulations show that a higher work function in tungsten-doped indium oxide (IWO) improves hole extraction in the perovskite subcell. In comparison, a lower work function enhances electron transport in the silicon subcell. To address this, a dual IWO interlayer with a graded work function is engineered via reactive plasma deposition by tuning the oxygen-to-argon flow rate ratio. This resolves interfacial mismatches and promotes carrier recombination. Furthermore, the optimized IWO surface facilitates improved anchoring with [4-(3,6-dimethoxy-9H-carbazol-9-yl)butyl]phosphonic acid (MeO-4PACz), thereby enhancing the quality of the perovskite layer. As a result, the optimized device achieved a power conversion efficiency (PCE) of 31.91%. This silicon-centric approach offers a scalable fabrication route for high-efficiency tandem solar cells.