From Bottleneck to Breakthrough: A Materials-Interface Roadmap for Commercial Monolithic All-Perovskite Tandem Solar Cells

All-perovskite tandem solar cells (APTSCs) promise >40% theoretical efficiency and the lowest levelized cost, but monolithic two-terminal (2T) devices remain below their potential. We show that the bottleneck is simultaneous optimization of three synergistic elements: (i) a 1.75–1.8 eV wide-bandgap top subcell whose Br/I-rich phase segregation must be suppressed; (ii) a 1.2–1.3 eV Sn-Pb bottom subcell whose Sn2+ oxidation and unbalanced crystallization and enrichment of surface/interface defects can lead to severe recombination losses; and (iii) an interconnect layer that must provide ohmic, transparent, and chemically robust recombination while withstanding perovskite-processing solvents and thermal stress. By synergistically tuning compositional gradients, stabilizing additives, and hybrid interconnect layers, future work should target simultaneous suppression of phase segregation and complex defect formation while maintaining scalable, low-temperature processing, thereby establishing a unified materials–interface framework to close the efficiency–stability gap for APTSCs.