A coordination trick keeps wide-bandgap perovskites from splitting apart

Researchers report perovskite/organic tandem cells at certified 27% efficiency with markedly improved stability.

Researchers reported in Nature on 27 July 2026 a method for making phase-homogeneous mixed halide perovskites, addressing a long-standing failure mode in wide-bandgap solar films. Those films tend to segregate into iodine-rich and bromine-rich phases because the two nucleate at different rates, degrading performance under light.

The team introduced a selective coordination principle: a molecular dipole tunes the local Lewis-base hardness at the donor atom, so a harder oxygen donor preferentially binds the harder lead in the bromide component. That slows bromine-rich nucleation to match the iodide side, yielding compositionally uniform films. They built cells at 1.62, 1.68, and 1.88 eV bandgaps that held 1500 hours at or above T90 under one sun at 65 degrees Celsius. A perovskite/organic tandem with an infrared-active organic cell reached certified 27.0% efficiency (26.4% steady-state) and T91 stability of 1000 hours under an ISOS-L2 protocol at 65 degrees.

Stability, not peak efficiency, is the wall that keeps high-performance tandem perovskites out of the field. If phase segregation can be suppressed by chemistry rather than exotic processing, it moves cheaper high-efficiency solar closer to something durable enough to deploy, which lowers the cost of electricity over time.

The figures come from lab-fabricated cells, and Nature notes this is an unedited early-access manuscript that may contain errors. Watch for independent replication and whether the stability holds at module scale and over years rather than hundreds of hours.

Source: Nature