Self-trapped emissions in 2D lead-free halide perovskites driven by divalent spacer cations.

The mono- and divalent spacer cation investigation in sodium/indium-based 2D double perovskites revealed significant impacts on optoelectronic properties due to distortions in the inorganic layers. The strong electron-phonon coupling in a novel lead-free Dion-Jacobson phase highlights a promising class for broad-emission devices based on self-trapped excitons (STE), offering enhanced structural stability.