Towards Intermediate Phase-Assisted Perovskite Crystallization via Aqueous Solution for High-Performance Solar Cells

Halide perovskite absorbers are promising materials for next-generation perovskite solar cells (PSCs), which rely on a solution made of several chemicals dissolved in toxic solvents. Such precursor solution processing is not compatible with a green chemical route. Aqueous precursor solutions are cost-effective and eco-friendly fabrication protocols; however, their device performances are inferior to those in regular. Here, an effective means of making high-performance PSCs is reported, enabled by proposing a doping strategy that incorporates RbCl into the Pb(NO₃)₂ aqueous precursor. The incorporation of RbCl into the Pb(NO₃)₂ film can form two intermediate phases, namely Pb(NO₃)₂·RbCl and (PbI₂)₂RbCl. The formation of these intermediate phases spontaneously facilitates the transformation of the resultant PbI₂ from a stacking layered structure into discrete [PbI₆]⁴⁻ octahedra. This promotes the coordination of A-site cations with the [PbI₆]⁴⁻ octahedra, thereby accelerating perovskite crystallization and reducing the residual Pb(NO₃)₂ or PbI₂. Hence, RbCl-doped PSCs exhibit excellent long-term stability, retaining 96% of their initial power conversion efficiency (PCE) after 2016 h under ISOS-D-1I protocol, and achieving a PCE of 22.75% with a fill factor (FF) of 82.62%. To the best of knowledge, this represents the highest reported FF and one of the highest PCE for PSCs fabricated from aqueous solutions.