Wide-bandgap perovskite with homogeneous crystallization and suppressed halogen segregation for efficient perovskite-organic tandem solar cells

The differences in crystallization and migration barriers of iodide and bromide within wide-bandgap perovskite result in inhomogeneous crystallization and halogen-phase segregation, limiting photovoltaic device performance. Here we report a sequential regulation engineering to synchronously homogenize crystallization and stabilize crystallographic phase by adding 2-iminothiolane (ITA). ITA priorly undergoes an in situ thiolation reaction with methylamine to yield a reductive 4-mercapto-N-methylformamidine (MMF). It effectively modulates perovskite crystallization toward homogenization, scavenges the detrimental molecular iodine or iodine radicals by redox reaction, and anchors the migratory iodide ions by hydrogen-bond interaction. Leveraging these contributions, the obtained perovskite films exhibit the suppressed halogen phase and enhanced ion migration barrier along the vacancy and interstitial defects-depending migration paths, achieving an efficiency of 20.45%. Moreover, the corresponding champion tandem solar cell (TSC) achieves an efficiency of 28.20% (certified 27.82%), retaining 90% initial efficiency by continuous tracking maximum power point after 700 h under ISOS-L-1 protocol. Inhomogeneous crystallization and phase segregation in wide-bandgap perovskite limit the performance of photovoltaic device. Zhu et al. develop an in situ sequential regulation strategy for crystallization, achieving a power conversion efficiency of 28.20% for perovskite-organic tandem solar cells.