Impact of Halogen Groups on the Properties of PEA-Based 2D Pb-Sn Halide Perovskites

Tuning broadband photoluminescence (PL) emission in 2D Pb-Sn halide perovskites (HPs) is vital for advancing optoelectronic applications such as color-tunable and white-light-emitting devices. These emissions, linked to structural factors like defects and phase segregation in the Pb-Sn system, are influenced by the molecular properties of spacer cations. Halogenation of spacer cations offers an innovative route to modulate molecular properties, enabling enhanced functionality in HPs. However, the sensitivity of broad emission to spacer chemistry remains underexplored.
In this study, we investigate the impact of fluorinated (4F-PEA) and chlorinated (4Cl-PEA) spacers on the emission characteristics of 2D Pb-Sn HPs using a high-throughput automated workflow. Our results demonstrate that 4F-PEA narrows broadband PL emission, reduces phase segregation, and mitigates defects, including microstrains. These improvements are attributed to the dipole-enhanced surface coordination provided by 4F-PEA, which stabilizes the lattice and suppresses non-radiative recombination centers. In contrast, 4Cl-PEA increases phase segregation and broadens emission due to its larger ionic radius, which induces greater lattice distortion. We synthesized 288 compositions of Pb-Sn HPs and analyzed them using hyperspectral photoluminescence and advanced machine learning methods. The findings reveal a correlation between the Pb:Sn ratio, spacer chemistry, and emission properties, highlighting that fluorinated spacers enhance optical performance and structural stability. X-ray diffraction and X-ray photoelectron spectroscopy analyses further confirm improved crystallinity and reduced defect density in 4F-PEA-based films.