Efficient Wide-Bandgap Perovskite Materials for All-Perovskite Multijunction Solar Cells

All-perovskite multijunction solar cells promise to deliver power conversion efficiencies (PCEs) beyond the theoretical limit for single-junction devices at low costs. However, the sub-par performance of the wide-bandgap perovskite limits the efficiency gains of tandem solar cells. In this contribution, we unveil localized compositional heterogeneity as a crucial factor in limiting the performance and longevity of wide-bandgap perovskite solar cells. We present our newest mitigation strategies using templated growth of Br-rich perovskites to improve their halide homogeneity and photostability, improving the open-circuit voltage to above<i> </i>85% of the theoretical limit from 1.8 to 2.3 eV optical bandgap. We demonstrate efficient all-perovskite 2J, 3J, and 4J solar cells, each presenting PCEs beyond 27% at 1 cm² device area.