Confining iodide migration with quantified barrier for durable perovskite solar cells

The migration of iodide ions out of the perovskite film degrades charge transport and electrode layers, reducing the long-term stability of perovskite solar cells. The current strategy primarily employs blocking layers atop the perovskite film to suppress this migration. However, the layers cannot completely prevent ion movement due to trade-offs with carrier transport. In this work, we quantify the barrier energy required to prevent the iodide ions migration from the perovskite film and develop a composite layer that leverages scattering and drift effects on perovskite surface to meet this threshold, reducing ions migration by 99.9%. Moreover, we utilize Poly(N-vinylcarbazole) with a high work function as hole transport material to address the band shift caused by the drift electric-field, thus enhancing hole extraction efficiency. Eventually, the device achieves a certified steady-state efficiency of 25.7% and maintains >95% of the initial efficiency after 1500 hours at 85 °C under maximum power point tracking. The blocking layer atop perovskite film cannot completely prevent ion movement due to trade-off with carrier transport. Here, authors develop a composite layer and use poly(N-vinylcarbazole) as the hole transport material, achieving certified steady-state efficiency of 25.7% for stable solar cells.