Impact of Ion Migration on the Performance and Stability of Perovskite-Based Tandem Solar Cells

The stability of perovskite-based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and all-perovskite TSCs using scan-rate-dependent current–voltage (J–V) measurements with drift-diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion-freeze power conversion efficiency from >31% for Si/perovskite and >30% for all-perovskite tandems to ≈28% in steady-state. Moreover, the ions cause a substantial hysteresis in Si/perovskite TSCs at high scan speeds (400 s⁻¹), and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all-perovskite tandems, subcell-dominated J–V characterization reveals more pronounced ionic losses in the wide-bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite-based TSCs which helps to separate ion migration-related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stability.