Synergistic Improvement of Bandgap and Crystal Quality for Highly Efficient and Stable Perovskite/Silicon Tandem Solar Cells

Wide-bandgap perovskite materials are essential for tandem solar cells (TSCs); however, Br-rich soft lattices may induce severe ion aggregation and migration, significantly compromising both device efficiency and stability. Based on the theoretical study indicating that Br– aggregation reduces the ion migration energy barrier, we experimentally demonstrated that precisely adjusting the perovskite bandgap from 1.68 to 1.65 eV effectively suppresses Br– aggregation, significantly increases the ion migration energy barrier and substantially enhances the photostability, all while maintaining the efficiency of TSCs. Furthermore, we lower the diffusion coefficients of both Pb2+ and I– during crystallization by designing functional molecules that incorporate multiple hydrogen bond donors and Lewis base moieties, thereby optimizing crystallization kinetics and mitigating residual stress. As such, the perovskite films with improved crystal quality exhibit an elevated ion migration energy barrier and enhanced carrier extraction dynamics at interfaces. These synergistic effects enable single-junction perovskite solar cells to achieve an efficiency as high as 23.24% and monolithic perovskite/silicon TSCs to reach 30.16%, while concurrently exhibiting exceptional stability under thermal, humidity, and illumination stresses. These findings offer valuable insights into overcoming the intrinsic limitations of wide-bandgap perovskites and provide guidance for the rational regulation of crystallization kinetics.