Phase-homogeneous mixed-halide perovskites for stable tandem photovoltaics.

Selective coordination of PbBrx and PbIx phases creates phase-homogeneous mixed-halide perovskites, enabling stable tandem solar cells with efficiencies over 27%.

• Why it matters: Phase segregation in mixed-halide perovskites causes instability and limits their use in tandem photovoltaics, necessitating strategies to achieve uniform composition and enhanced durability.
• What they did: A molecular dipole approach tunes local Lewis-base hardness at the donor atom, selectively retarding Br-rich nucleation and synchronizing it with I-rich phases in the perovskite film.
• The result: This method produces compositionally uniform wide-bandgap films with improved efficiency and stability, leading to tandem cells with 27.0% efficiency and 1,500 hours of operational stability.