Stable Inverted Antimony–Bismuth Alloyed Inorganic Perovskite Solar Cells via Crystallization Control and Defect Passivation

Abstract

Triple-junction tandem solar cells require top-cell absorbers with suitable wide-bandgap (2.0–2.3 eV), low toxicity, and high stability. Bismuth-based perovskites with the A3B2X9 structure have emerged as promising candidates due to their nontoxic nature and favorable optoelectronic properties. However, their efficiency is constrained by intrinsic deep-level defects, low-dimensional morphology, poor film quality, and mismatched energy alignment with charge transport layers. Here, we address these challenges using an antimony–bismuth alloyed Cs3SbBiI6Br3 perovskite as an absorbing layer. Incorporating methylammonium chloride (MACl) into the precursor solution yields mixed-halide films of Cs3SbBi(I,Br)9–xClx, retarding crystallization and enhancing both film quality and two-dimensional phase purity. Furthermore, we introduce potassium hexafluorophosphate (KPF6) on the films. KPF6 forms a dipole layer on the surface, which upshifts the perovskite Fermi level and suppresses defect-mediated recombination. The resulting inverted (p–i–n) devices achieve a champion power conversion efficiency of 1.8% and an open-circuit voltage of 0.88 V, which is the highest reported for A3B2X9 perovskites in inverted architecture. Moreover, the KPF6-treated devices retain 90% of their initial efficiency after 3200 h of storage in nitrogen, demonstrating exceptional stability. Our work highlights the potential of Sb–Bi alloyed perovskites as top-cell absorbers for triple-junction tandems.